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Water Storage Book Index

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access (tank)  9,53,55,56,57,109

form for  102

hatch  117

lockable  52

pressure-tight  56

sealing  52

Acrylonitrile Butiadene Styrene (ABS)  94

ac (acre)  90

additives  39

aerator.See inlet aerator

aesthetics  31

afy (acre-feet per year)  90

agricultural chemicals  23

air, displaced  8

airlock  9

air gap  55

air pressure level gauge  70-89

air vent.See vent, air

alarm  35,71

algae  9,22,27,65,76

aluminum  43

animal droppings  9

anti-seep collars  25

apartment  88-89

appropriate technology  3

aquaculture  21,23

aquatic plants  21,27

aquifers  16-20,76,88

artesian  18

confined  18

contamination  17

fissured  18

gravity  18

high  22

increasing water in  19-20

injection wells  19

overdrafting  19,83

perched  18,83

protecting quality  20

recharge  7,19,21

saltwater intrusion  18,19,20

subartesian  18

types  18

architectural guidelines  52

area, formulas for  90

Arizona desert  88

armature (for ferrocement)  95,107,114,117

atm (atmosphere)  90

attrition (of pathogens)  2,10,11


bacteria  5,9.See also pathogens

anaerobic  10

a health problem?  11

fecal  7

indicator  13

bacteria, beneficial  72

bacterial regrowth  11,12,76

baked enamel.See porcelain-bonded carbon steel

ball valve.See valves, ball

bathing  7

bathtubs  7

beavers  27

bedrock, fissured

and  23

bending force  91,92,93

bentonite clay  24,61,109

biological hazards.See pathogens

birds  22

bisphenol-A  94

boilers  11

bore.See wells

Branched Drain Greywater Systems  124

brass  41,42

brass fittings  56,114

break pressure tanks  54

brick (tank material)  44

bucket  56

Builder's Greywater Guide  124

building department  52

bulkhead fitting  45,87

buried storage  31,38,44,47,49,65,74

collapse of  32

burning brush  79


calcium, precipitation  11

capillary connection  16

cedar  45

cement  6

cement mixer  108

cheap and easy  8

check valve.See valves, check

chicken wire  117

chlorination  9,10,12,27,67,76

cigar shape  32

circumference of a circle  90

clarified septic effluent  10

clay (material for storage)  22,44

clear tube (as level indicator)  70-89

climate  20

cold joints (in concrete)  107

coliforms.See bacteria

coliscan plate  11

color coat  106

combined drain/outlet.See drain, combined with outlet


overview  28

spreadsheet  28

compound curves.See curves, compound

compression force  92,93

concrete  11,22,32,44

fly ash in  39

forms  96-107

conduction  54

confining layers  18

conical floor.See floor, conical

conjunctive use  19


in emergency  35

contact time  12

contamination.See toxins

context  3,14,95

convection  54

conversions  90

copper  42-43

pipe  54

corks  62

corrosion.See rust

cost  5,8,16,22,24,27,50-51


really cheap storage  50

cost-benefit  4

Costa Rica  88

CPVC  54

crayfish  27

Create an Oasis with Greywater  124

creeks  14,18

creek direct.See source direct

critter-proofing  8,50,63,64,65

crud  8

Cuba  54,58

curing  96

too fast  100

curves  71

compound  93,116,117

simple  93

cut  48


dams  20

dead storage  55

decorative   75

deflocculation  10

demand.See water


contexts  6

ecological  3

life  7

principles  3-8

trade-offs  4

disaster  1

sizing storage for  35

disinfection  11

byproducts  10,12

decay  12

dissolved oxygen.See oxygen

distribution system  10

diversions  23,25,83,85

dobies  108,113

size  115

drain  58-62

capped  59,60

center  111

combined with outlet  45,58,60

construction details  61,109

extension  71

for buried tanks  31

for pond  24,25

in wood tank  45

location  59-65

low tech  61

options  61


plastic tank  60-65

steel tank  58,59

size  62

sump  60-65,104

drainage  48

dredging  27

drinking water  7,88

emergency  76

seperate system  6

drought  19

drowning hazard  9,27,53

drums  6,50,76,89


earthquake  2,35,53,77-89,89

earthquake loads  91

ecological design.See design, ecological

economics.See cost

Eden  88

electricity  1

dependence  89

electric heater  74

electrolytic corrosion  42,43

electronic level indicator  70-89

embankment  26


reserve  35,52,56,73

storage  75-89


consumption  6

thermal  2

engineer's stamp  52

engineering  53,77

EPDM  22,23,24,46,94

epoxy-coated rebar  57

epoxy-coated steel  47,94

erosion  24

Ethylene Propylene Diene Monomer.See EPDM

Evans, Ianto  13

evaporation  2,16,20,23,23-24,27

swimming pool  27

evaportranspiration, vs precipitation  20

excavation  101-107

expanded metal lath  92,113,114,117


failure  8

fecal matter  11,12.See also bacteria, pathogens

fences  78

ferrocement tanks  41,57

construction  95-120

experimental improvements  96

forms for  96

heavy-duty  107-120

light-duty  101-103

medium-duty  104

skill required  95-107

spherical  96

tank shape  38

ultra-light-duty  100-101

fiberglass (glass fiber-reinforced polyester)  32,46-47

footings for  49

field capacity  15,16

fill  48,60

fillet  92

filtration  10,66,124

fire  1,2,124

department  52

fighting  52,78-81

hoses  1,79-89

hydrant  2,35,52,55,73,79,80,81,83

reserve  34,56

resistant storage  77-89

safety  21

sprinklers  2,80-89,89

trucks  81-89

fish  21,22,24

in   26

nuisance  27

floating solids  8,62

float (level indicator)  69-89

float switch  71

float valve.See valve, float

flooding  2,24,25,53

hazard  52

plains  21

reduction  16

floor  48-49,55

concrete  38

conical  92,112

construction  105,109

dished  92,112

finishing  116

flexible  91

options  61

pouring  115-116

pumping  115

shape innovations  112

slab  113,115

sloped  60

stiff  91

strain  49

Thai jar  97-107

flow.See water/flow

foam injection  36,79,81-89

footings  48-49,102-107

Thai jar  96-107

forms.See concrete, forms

fossil fuels  3

foundation.See footings


hydroelectric  29

freeze protection  1,2,73-75

by burial  31

pond depth  24

frost heave  32,91

ft3/sec (cubic feet per second)  90

fungicides  39


gallons per inch  70-89

galvanized steel  8,41-42,56

corrosion.See rust

welded tank  64

with plastic membrane  47-48

galvanizing paint  56

gal (gallon)  90

Gambusia.See mosquito fish

garden hose  79

gasoline  78

gasses, disolved  11

gate valves.See valves, gate

generator  79

geology  18

glass  39

glass reinforced polyester (GRP).See fiberglass (glass fiber-reinforced polyester)

goals  1,4,5

goat bladders  48-50

gpm (gallons per minute)  90

grading  105

gravel (as footing)  48


flow  29,55,66

loads  91

gravity flow water systems  120

Greenpeace  45


storage  6

greywater systems

for runoff harvesting  16

grid  111

groundwater.See aquifers

gauge.See pressure gauge

gutters  42,65,80


hardness  12

hardware cloth  92,114,117

hazards  52-53

biological.See pathogens

liability.See liability

ha (hectare)  90

HDPE  46,76

cast into masonry  61

taste  46

toxicity/leaching  46

health department  52


effects  10-11

heat loss  54

high density polyethylene.See HDPE

hilltops  31

hog-ring pliers  107

pnuematic  107,117

homeowners' association  52

hoops  113

spacing  114

stress  92-96,113

hot springs  54

drain  62

hot tubs  75,81

hot water storage  54,75

Huehuecoyotl Eco Village  11,16,25,83-84

hurricanes  2,77-89

hydrant.See fire hydrant

hydroelectric  14,16,83-84

battery  2

pressure for  29

hydrogen sulfide  67


ice-skating  21

ice loads  91

indoor supply plumbing

copper  42

infiltration  15

basins  7,19,21

coefficient  19

galley  87

inlet  12,55,55-56,58

aerator  10,67

combined with outlet  66-67,67

diffuser  67-68

float  73

float valve.See valves, float

hidden  104

in roof  56

welded  56

insulation  74

insurance  52

Intermediate Technology Development Group  96,101

iron  12,67

irrigation  6,7,16

covering peaks  34

drip  7

storage in soil for  15-16


Kemnitzer, Paul  107,120

kitchen sinks  30

kPa (kilopascal)  90


ladder  9,53,56,57

built-in  117

Lake Cachuma  24

landslides  31,53

lath.See expanded metal lath

laundry  7,75

leaching.See toxins, leaching

lead  39

based paint  9

glaze  44

leaks  9,23,27,56,61,68

in wood tanks  45

leather  48-50

legal requirements  1,2,5,52,67

firefighting  36,78

levees  22,24,25

construction  25

cross section  26

level indicators  69-71

lexan.See polycarbonate/ lexan (PC #7-other)

liability  5,21,53

lid  9

removable  27

lifestyle accommodation  4

lightning  77

lights  115

lime  12

livestock  7,21,24,26

loads.See structural loads

locks  78

long-term storage  76

Los Angeles  89

Low-Density Polyethylene (LDPE #4)  94

low pressure.See pressure, low

lpm (liters per minute)  90

L (liter)  90


m3/day (cubic meters per day)  90

m3 (cubic meter)  90

manganese  67

manhole.See access (tank)

marine plywood  45

market culture  3,5

Maruata  16-18

masonry  60

masonry in and over plastic  47

materials  28,39-48

efficiency  36,38

toxicity  12

to avoid  39

membrane  92

meter  66

Mexico  83,93

microclimate  21,74

mold.See concrete, forms

mold-release agents  39


screened  55

mosquitoes  9,22,27,52,63,65

fish  27,124

trap  52

multiple tanks  7,72

plumbing options  73

muskrats  25,27

m (meter)  90


Nalgene bottles  94

National Drinking Water Clearinghouse  120

National Fire Protection Association  120

National Testing Laboratories  120

natural pools  27

natural resources

waste  33

natural swimming pools  120

New York City  88-89

Nil  102

nitrates  20,23

non-modulating float valve  120

NSF 61 certified  39,46,47

cement  41

sealers  41

NTU  90


and algae  27

in water  65


oak  45

odor  12

organic mater  9

outlet  9,12,35,56

curves  71

float  68

for pond  24

screen  68

overflow  9,25,52,55,62-65,71,73

critical  64

for pond  24

line  63

size  62

uncontrolled  9

oxygen  67

for fish  26

ozonation  2,10,71,76


paint  12

reflective  65

with zinc  41

pallet wrap  108

pasteurization  10,11

pathogens  10,12,13,53,72.See also bacteria

pebble tech  27

perched aquifer  18

perfectionism  109

performance standard  4,5

inflation  4

permeation  11,53,76,78-89

permit.See legal requirements

pesticides  13

in aquifers  18

PETE.See Polyethylene Terephthalate (PETE or PET #1)

pH  12,26

pipe  29

abandoned  12

nipples  8

size  1


size  32

wrap  109

planes  93

plants.See irrigation

plaster  113

color  119

curing  119

in tension  92

mixer  108,118

plasticizers  39

plastics  65

American Plastic Council  45

health & ecological issues  94

membranes, coatings and bladders  48


drain retrofit  60-65

footings for  49

tank material  45-46

tank shape  38

taste  46,76

plumbing  11

code  52

for easy changes  8

point loads  91.See loads, point

polyamide epoxy.See epoxy

Polycarbonate/ Lexan (PC #7-other)  76,94

polyethylene  54

septic tanks  32

Polyethylene Terephthalate (PETE or PET #1)  46,76,94

Polypropylene (PP #5)  94


clay core  25

combination  22

cost  25

depth  24

duck  6

embankment  22

excavated  22

failure  22,25

liners  24

living  21,22

locating  21

runoff harvesting  21,22

shape  24

size  24

storage  21,22,23

turn over  24

types  21

wall slope  24

weeds  24

Popocatepetl  93

population  7

pot growers  51

power outage  35

pressure  6,8,29,36,91

for different applications  30

gauge  66

as remote level indicator  70-89

inward, from burial  32

loss in tank  33

low  29

maximum  29

spike  69

switch  71

tanks  29,30,38,54

very low  87-88

Principles of Ecological Design  124

progress, true  3

psi (pounds per square inch)  90

pump  30,56,88,89

buried tanks  31

for fire  79

for pressure tank  54

pumping  1,2,3,6,15,19,20

downhill (pet peeve)  32

energy use  30

pump control  71

purification.See treatment

PVC  8,45,46,51

in sunlight  9,39

pipe  14


raccoons  76

radial with hoops  111,116

radio links  29,71

rainwater  7,27,76

cistern under an office  64

fate of  15

gutters.See gutters

harvesting  12,72,83,88,96

Huehuecoyotl  83

tank for  101

infiltration  16

Rainwater Catchment Systems for Domestic Supply (book)  120

Rainwater Harvesting & Runoff Management  7,15,19,21,50,84,124.See also runoff

rats  9,65,76

rebar  92,113

hickey  107

joining  114

overlap  114

spacing and size  92

welding  114

recycling  8

redwood  27,45,77,92

red cedar  39

regulations  i

reliability  8

repair  8

reserve.See emergency, reserve

resource use  3

riprap  25

river  81

rocks  11

tank shape  38

rock and mortar.See stone tanks

roofs  50,116-117

cave-in  118

center pole  117

conical  38,50,57,92

domed  38,50,91,92,93,116

construction  102-107

flat  50

grid  117

hexagonal  50

water harvesting  50

roots  49,77-89

as pumps  15

rope  53

runoff  7,15,20,21,23,25,56,83

rust  41,48,58,63


sacred spots  31

safety factor  92


flushing  7


filter  72,86

silica  119

sand filters  120

San Juan Island  72

screed  116

security  31

and tank size  32,33

standard  4

sediment  9

septic conditions  12

septic tank  10,44

outlets  63

plastic  32

set-aside.See reserve;See also emergency, reserve

settleable solids  86

settling  2,8,10,11,73

inlet diffuser for  67

sewage  10

in aquifers  18

shade  65

shape  36-38

for burial  32

graphical overview  36

rectangular  9,36

rock-like  117

sphere  32,36,38

square  36

structural effect  93

shear force  92,113

shower  1

shut-off valve.See valve/shut-off

silver solder  54

sinkholes  19

siphon  55


prep  109

walk-in only  109

siting  28-32


structural effect  93-96

sizing  32-36,44

for firefighting  36

for intermittent production  35

for interruptions in supply  35

for limited supply  34

skimmer  27

skinny-dipping  78

slab.See floors, slab


stability  29,31

steep  53

sludge  58

small containers  76

smell  12

snow load  93


loads  91

report  52

storage in  15-16,25

vs aquifers  15


greenhouse  2

heaters  75

source direct  14-15,85,85-87

specific heat  2

spillways  25,64

spill point  55

springs  1,2,9,12,14,16,18,22,23,34,66,85

stainless steel  42,54

standpipes  79


reinforcing  95

tanks  48

tank shape  38

Stinson Beach  15

stone tanks  43

storage .See , storage


uniform  93

structural loads  53,91-93,91-96

buried  31

collapse  53

considerations  91-93

efficiency  36

point  116

stucco.See plaster

subsurface irrigation.See irrigation/subsurface

suburban house  89

sulphur  12

sun, on tanks  9

sunscreen  47,65

by burial  31

supply  66.See water/supply

surface area, formulas for  90

Surface Water Treatment Rule  120

suspended solids.See turbidity;See also floating solids;See also settlable solids

swamp coolers  2

swimming  22,124

holes  11

pools  27,75,81,89

aboveground  27,51

variable level  27

swing joint  80

system modes  28



cleaning  58,59,60


toxins in  39

cost.See cost

forces on.See structural loads

galvanized.See galvanized steel

multiple.See multiple tanks

on roof  29

open  27

painting.See paint

shape.See shape

siting.See siting

sizing.See sizing

Tank Talk Newsletter  120

tannins  22

tap station  98

taste  12

temperature  12,65

of buried storage  31

tension force  92,93

Thai jar  96-98

thermal mass.See specific heat

thermal storage  1,2

thermos  54

Thoroughseal  106,116,119

toilet  7

flushing  7

tank  75

tools  107-108

torque block  59

tote bins  51

tower.See water, towers

toxins  7,9,53,78

leaching  11,12,53,76

PVC  39

threat to aquifers  20

transporting water  54-58

trash cans  39

treatment  2,73,124

biological  27

residual  10

trees  77-89

triangles  93

trihalomethanes  9,10

tunnel vision  3,5

turbidity  7,12,67.See also floating solids;See also settlable solids

and fish  26

turbulence  71


ultraviolet light  10

underground river  17-18

union  56

units.See measurements


vacuum breaker  25


ball  62

check  55,56,63

float  55,66,71

gate  69

shut-off  55,56,61

vandalism  78

variable height outlet  68

vector control  52

vent  55,65

vermin  27

vernal pools  22

volume, formulas for  90


walls  91,102-107

floor joint to  113

structural loads  92

thickness  92

washing machine  7


age  12

bottled, survey  12

color  12

corrosive  12


forcast  7

flow  1

hazards.See hazards

level  105,107

pressure.See pressure

protecting  77

quality  1,2,4,12,16,83

changes  9-13

guidelines for different uses  7

improving  10

of   20,23

separate handling  6-7

testing  12-16

quantity  5

running  6

security  1,1-2

shortage  1,19

softness  7,12

stagnant  12

still  6

stored energy  2

supply chain  1

taste  7

temperature  12

towers  29,38,53,54,66,77

safety  30


covering peaks  33-34

hourly  34

peaks  1

per capita  6

waterbed bladder  39,48

Watermaster  120

watershed  16,18,20,25

area for   23

water age  120

water hammer air cushions  68,69

Water Quality Testing Procedures and Information Packet  124

Water Storage Extras  124

weather station data  120

welded steel  60

wire mesh  109

wells  9,17,18,55,66,82.See also aquifers

artesian  16,18

contamination  55

horizontal  16,87

low yield  34

wildlife  22

and   26

habitat  21

Willard  107

wind.See hurricanes

wind loads  91

wings (for rain harvesting)  116

wood (tank material)  45


yucca stalk  61


zinc  42

zoning  52





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SeeWater Storage-bookmain page


Chapter 1: Thinking About Water To achieve your design goals water system, it is helpful to know what your goals are. first order of business is to consider: Why Store Water? Nearly all water systems include some form of storage, most commonly tank. Storage can be used to: cover peaks in demand smooth out variations in supply provide water security in case of supply interruptions or disaster save your home from fire meet legal requirements improve water quality provide thermal storage freeze protection enable smaller pipe to serve distant source We're going to consider each of these reasons to store water, then look at design principles to help you frame goals your project. Cover Peaks in Demand most common function of water storage is to cover short-term use flows that are greater than flow of water source. example, tiny, one gallon-per-minute spring supplies 1440 gallons day. This is several times more than most homes use in day. However, almost every fixture in home consumes water at faster rate than 1 gpm while it is turned on. Even low-flow shower head uses about 1.5 gpm.m By using water stored in tank, you can supply water to shower faster than it is flowing from spring. On completing shower, water will be coming in faster than it is going out, tank level will rise back up. If you had 10,000 gal tank, you could run 100 gpm fire hose--creating kind of blast used to bowl over hostile crowds--on stored water from this tiny spring, hour half! Hopefully fire would be out by then, as tank would take several days to refill. Smooth Out Variations in Supply In some circumstances, your storage needs will be affected by variations in water supply. instance, if supply is rainwater, you will need enough storage to make it through intervals between rainfalls. six-month, rainless dry season requires heck of lot more storage than most common kind of variable supply-- well pump that cycles on off. If you have well that taps stored groundwater, tank will save wear tear on your pump, because pump won't have to switch on off every time you open tap. Provide Water Security in Case of Supply Interruptions or Disaster In many places, water supply chain from source to tap is long made of many delicate links. If cow steps on supply line, pump breaks, wire works loose, electricity goes out, city misplaces your check, or there is natural disaster, your water flow could stop. By locating your storage as few chain links away as possible from your use point, large measure of security is added: In case of earthquake, hurricane, flood, etc., storage can be slowly emptied to meet essential needs until service is restored. If your well or electrical pump goes out, or your spring lines wash out, storage you have water until you can get it fixed. Save Your Home from Fire Designing system to be effective combating fire can change its specifications radically. To put out fire, your stored water needs to be available at flow rate many times greater than normal. (If you want your system to have this capability, see Systems Firefighting, p. 78.) Meet Legal Requirements Sometimes you may be required to install water storage simply to meet legal requirement. On other hand, you may be able to trade increased water storage slack on different legal requirement. example, if you provide large amount of water good pressure that is reserved fire emergency, sprinkler system, /or hydrant, fire department might allow you to build narrower driveway smaller turnaround further from house than they would otherwise--thereby saving you fortune. Improve Water Quality water coming out of properly designed tank can be of significantly higher quality than water that goes into it. This is mostly due to attrition settling (see Ways to Improve Water Quality in Storage, p. 10). Add ozonator, tank becomes substantial treatment step (see Ozonator, p. 71). Provide Thermal Storage Freeze Protection Water has higher specific heat--stores more thermal energy per unit of weight--than any other common material. large thermal mass of water stored within solar greenhouse or home can help to keep it cooler in day warmer at night. Also, as water changes to ice, it radiates tremendous amount of stored energy. Imagine how much gas it would take to melt water tank-sized ice cube; water freezes, it releases this same amount of energy. This is why irrigating frost protection is effective. stored energy in water can prevent water tank or nearby components from freezing (though in coldest climates this may not be sufficient--see Freeze Protection, p. 73). Evaporation consumes even more energy, is why swamp coolers cooling towers are effective. Water is also effective heat transfer medium. Finally, in rare instances it can be economical to use elevated water storage as Ïbattery," from electricity is extracted by running it through hydroelectric turbine. Enable Smaller Pipe to Serve Distant Source If flow of your source exceeds peak demand, you can connect to it directly without storage. However, if source is distant, it may be cheaper to run small pipe to nearby storage, big pipe from there to use point. small pipe would be sized to average use, big pipe to peak use. savings in materials labor from running smaller pipe over most of distance can often pay storage then some. Design Principles This book sees water storage through lens of ecological systems design-- view that is both global finely detailed. You don't need to share this view to value utility of material in this book or benefit from its application. However, ecological design approach offers so much advantage so many pressing issues, feel compelled to take moment to look at design of systems before diving into details of water storage. (If you are not in mood design philosophy, please skip ahead to Separate Handling Different Qualities of Water, p. 6.) Ecological Systems Design has been my day job since 1982. My focus since 1989 has been design of water wastewater systems. 've designed, built, studied water systems in twenty countries, covering many applications, in wide range of natural cultural conditions. designed my own major in Ecological Systems Design, completed at UC Berkeley. However, my most important insights have occurred in countless rugged miles 've logged exploring extraordinary wild water systems. 've become very aware of how water quality changes as it moves through natural engineered systems. This, my experience testing water have led to many realizations that have influenced designs in this book. My work-- life--are inspired by what call Principles of Ecological Design.1 In brief, to design ecologically, follow these principles: Transcend market culture. main obstacles to living nature are cultural, not technical or economic. Much of American culture has been designed by marketeers, is diametrically opposed to living cheaply ecologically. Follow nature's example. Natural water systems are vastly more sophisticated elegant than artificial ones. Pay them heed--they are gold standard. Intervene as little as possible. Choose inherently simplest solution, then implement it as well as possible. Remember that maintenance increases number of parts, that any moving mechanical part is itself many parts. Understand that context is everything. context must be known in order to determine if design is Ïgood" or not. There are no universal solutions. There are approaches patterns that can be applied to generate optimum solution in variety of contexts. Nature provides diverse solutions to all problems; she never repeats. Every branch of tree is different shape that fits its purpose exactly. Overcome tunnel vision. Design global, yet detailed view. market economy tends to promote tunnel vision, using exponentially increasing amount of money resources to get higher performance on narrow set of parameters, while whole withers. Use appropriate technology. Cleverly matching level of technology power of your tools to task at hand is cheaper, healthier, lower impact, more enjoyable--yet ultimately more powerful than any single solution. Practice moderate efficient resource use. Fossil fuels electricity have severed connection between energy source consumer. One thin pair of wires can silently channel unbelievable amount of energy to pump deep underground without creating ripple of awareness. This has enabled our relationship energy to skew way out of scale. (Consider how you'd conserve if you were walking down forty flights of stairs carrying water back up in buckets.) Empower users' awareness creativity. Design monitoring adjustment. We kid ourselves that our artifacts are immortal but they all fail time. Nature allows failures, using information to improve her designs building in flexibility changing conditions. Make true progress. Most of what is commonly called Ïprogress" is relocation of problems out of sight in space or time. True progress actually solves problems. Water System Design Here's what general ecological design principles look like applied to design of water systems: Minimize overall negative impact on natural social systems. easy way to do this is to spend as little money use as little water as possible. Create positive impacts-- example, by slowly releasing stored water to ecosystem during dry season. Leave as much of water work as possible to nature. Divert water just after evaporation or soil has naturally purified it so that it requires no further treatment. Divert water higher than point of storage points of use if possible, -- Conserve pressure in plumbing so that minimal or no pumping is required. Use adequately, but not excessively, sized pipe to reduce friction loss it matters, use pipe that's as small as possible friction loss doesn't matter. Design to extract benefit from other attributes of your water, e.g., nutrients, softness, temperature, pressure. Rigorously confine materials that are incompatible natural cycles (such as motor oil solvents) to their own industrial cycles. Add to water only cleaning products materials that biodegrade into plant nutrients or non-toxins. Add these materials in order that lets water cascade through multiple uses, from those that require cleanest water to those that tolerate dirtiest. Distribute nutrient-laden final effluent to topsoil on-site purification/ reuse. It is worth reflecting on these principles before you spend thousands of dollars on your water system. All design is art of trade-off. cost-benefit curve most design parameters shows diminishing returns. It goes up steeply at first, then levels off. However, trade-offs external costs continue to increase. If you push too far trying to maximize few parameters at expense of everything else, you will wind up less less total benefit. too narrow or fuzzy view, myopic push to maximize parameters in sight will inevitably compromise parameters that are not seen (see Tunnel Vision, at right). It is relatively easy to save water by wasting energy, or to save water energy by wasting materials money. It is relatively hard to make overall improvement. easiest ways to achieve this are to: get stay clear on big picture goals change specifications so that full range of effects are explicitly considered improve fit between subsystems decide what is least necessary cut it out make some lifestyle accommodation Performance Security Standard water system's performance security standard can be expressed as percentage of time system is Ïup." If your water is on nine days in ten, that's 90%. If your system is down three days year, that is performance security standard of 99%. If your water were off only one day every ten years, that would be 99.97% standard. performance security standard is relatively invisible design parameter. It is almost never discussed openly, even though it can influence design more than just about anything. Here in America, culture is fear-based, business interests dictate government policy, there tends to be runaway inflation in performance security standards. Our grandparents carried water in buckets from open well in backyard, yet we fear we'll die if tap isn't always capable of delivering way more sterile water than we need, at high pressure. my clients, always haul performance security standard out in open conscious consideration. You don't want to design having water 100% of time. To go from having water 95% of time to 98%, to 99%, to 99.5%, requires roughly doubling of expense environmental impact each increase. You need to take into account consequences of insufficient storage, your emergency supply options, environmental impacts, your budget to determine appropriate performance security standard your system. If it doesn't really matter much if you run out of water, why spend fortune on storage? Then again, if you have kidney dialysis machine or some other critical application, obviously you'll want to set security standard higher. Running Water People, Still Water People Worldwide, people who have pressurized water on tap use about hundred gallons day per capita. People who carry water use about ten gallons day to accomplish much same tasks. Most of difference is waste. It is easier to let tap run than to turn it on off. In contrast, still water just sits there serenely until you scoop it up. On typical construction site in industrialized country there are hoses spray nozzles--push lever water blasts out. In non-industrialized societies, there are typically couple of big drums buckets of water construction use. Since almost none of construction water needs to be clean, water is cascaded through various uses. example, tools that have been used adobe or cement are cleaned in drum, muddy (or cement-y) water is then reused to make adobe (or concrete). Water washing hands is scooped out of Ïclean" construction water drum, into bucket, then dumped into Ïmuddy" drum it is dirty. non-industrialized method has advantages both consumption disposal. water consumption ( energy consumption, if water is pumped) is fraction as much as in industrialized scenario. Also, instead of leaving giant toxic puddle of cement water, all cement water is incorporated into masonry work. (We are working on development of hybrid plumbing systems that combine convenience of pressurized water efficiency aesthetic benefits of still water.) Separate Handling Different Qualities of Water In many contexts it makes sense to use different qualities of water different purposes. Depending on water use, specifications (including those storage) may be quite different (see Table 1). If more than one type of water needs storage, storage will have to be separate. As kid, irrigated my first garden water siphoned from child's swimming pool that was used as duck pond. Clear well water went into pond, after week's storage, drew out thick, chunky, pea soup-looking water. garden, duck poop water was better than potable water. Drinking water requires most stringent specifications source, storage, security, but is used in smallest quantity. You might be able to make your life much easier by making separate system separate storage drinking water. ( example, see Creek Direct Sand Filter, p. 85.) Irrigation water has least stringent specifications water quality, storage, security, is typically used in largest quantity. It can be stored separately in inexpensive, high-capacity storage such as soil, ponds, or aquifers. Water irrigating fruit trees shrubs can be of lower bacteriological quality than water used irrigating vegetables consumed raw. Greywater (household washwater) should not be stored in tank more than 24 hours. It is best to route it to soil as it is generated store it there. (See our book Create Oasis Greywater/ Common Mistakes Preferred Practices.2) Rainwater from roofs is especially suited hair washing, laundry, flushing salts from soil, due to its extreme softness. In old days, inns would have pitcher of spring water drinking, separate basin of rainwater washing. It is prudent to plumb rainwater downspouts to your greywater distribution or irrigation system (if you have one) so soft rainwater can flush irrigation salts from soil, as it soaks in recharges groundwater. It is not necessary to have storage to do this; it is actually most effective to do it while it is raining. If you have separate rainwater harvesting tank, you can plumb it to supply washing machine bathtub, any extra going to toilet overflow to salt flushing. (See our forthcoming book Rainwater Harvesting Runoff Management.3) Runoff water is generally suitable only irrigation, flushing salts from soil, or groundwater recharge. (See Aquifers, p. 16, Rainwater Harvesting Runoff Management.) Table 1: Different Water Qualities Different Uses Contamination limits Use Fecal bacteria per 100 ml Turbidity Toxins Notes Drinking water sensitive humans 0 Almost none Almost none Needs to taste good Well-direct groundwater recharge 0 Almost none Almost none Drinking water resistant humans 10 Low Almost none Needs to taste good Drinking water livestock 300 Moderate Almost none Dishwashing water 300 Moderate Low Bathing water 300 Moderate Low Laundry water 1,000 Moderate Moderate Best if low in calcium, magnesium Toilet flushing water 1,000 Doesn't matter Moderate Irrigation of annual vegetables 1,000 Doesn't matter Moderate Groundwater recharge through mulch-filled infiltration basins 3,000 Doesn't matter Moderate Irrigation of fruit trees 3,000 Doesn't matter Moderate Subsurface irrigation 10,000,000,000 Doesn't matter Moderate Irrigation of non-fruit trees 3,000 Doesn't matter Matters least Drip irrigation 3,000 Almost none Moderate Will clog if it has lots of solids Warning: These figures are based on my observations of what is working in practice, depart radically from legal standards at points--follow them at your own risk. Our other water books articles have more information about different qualities of water different purposes.4 Design Horizon Water supply systems should typically be designed built 15- to 25-year life span. biggest variable over this time is often population. Population determines needed capacity tanks, pipe sizes, etc. If long-range water demands cannot be accurately forecast, shorter design span can be used. Note that providing abundant water tends to make population bloom, exerting feedback effect. One of best ways to account changes in future storage needs is to provide addition of more storage later-- example, in additional tanks (see Figure 26, Multi-Tank Plumbing Options, p. 73). Instead of putting your first tank smack in middle of one area tanks could go, put it to one side. Later, you'll be able to add more tanks next to it if necessary. Design Failure, Design Change Another key to good water system design is to consider how components will age, what to do they fail. Every piece of system is going to fail someday. Ask yourself what is going to happen it does. Will its failure be dramatic, or mundane? How long will it take to fail? Can failed part be accessed cleaning, repair, replacement, reuse, or recycling? Good design makes it easy to change system--to add another tank, new connection, valve, etc. As you're making original installation, picture your future self having to come back to expand or repair system, make it easy to do so. Take look at Figure 18, Drain Options (p. 61), example. You'll notice that sections of PVC pipe between fittings are long enough that you could saw through them in middle still have enough pipe on both sides to insert replacement valve, insert tee to another pipe line, or make some other change or repair without having to throw anything away. If fittings were all glued together Ïhub to hub," no exposed pipe between them, to change anything you'd have to throw everything away. Likewise, galvanized pipe nipples in Figure 18, Drain Options (p. 61) are smallest size that still allows pipe wrench to grip pipe. Shorter nipples are one-use; to get them out you've got to grip them wrench on threads, wrecks them. Stuff in Water Ends Up One key to good water system design is to focus less on water. Sure, water is significant. However, there is tendency to think that water is taken care of, design is done. Most designs fail to account adequately other stuff in water: materials that sink to bottom materials that float on surface materials that dissolve into or out of water air that is displaced by water water-seeking critters that crawl or fly into system Take care of other stuff, water will just about take care of itself. Moreover, your system will deliver higher-quality water more reliably, be less quirky, last longer. This is especially true if your design parameters are extreme in any way: lots of sediment floating crud, very low pressure, barely enough water, wild fluctuations in supply or use, etc. How do you design other stuff? It's easy: Not just water, but all stuff that comes along it ( air it displaces) have to go somewhere. Simply ask yourself, Ï are air, sand, leaves, rust chunks, mineral deposits, spiders, frogs, mosquitoes going to end up in my system?" Consider different design scenarios you'll find best overall disposition of water its companions. (See Figure 2, Common Storage Problems, p. 9.) What Do You Have? What Can You Find? In practice, people are likely to use tank they already have, or one that's sitting in boneyard down street, or tank that can be purchased easily inexpensively. This is true even if tank is considerably smaller or bigger, of another material, or otherwise out of sync theoretical ideal. Cheap easy weigh very heavily in practical terms. Salvage storage is often economically ecologically superior, if you can find it. One community know purchased used 50,000 gallon tank good price. This tank is made much better than brand-new, modern galvanized tank next to it. Even though it is decades older, it looks like it is going to outlast new tank. How Water Quality Changes in Storage quality of water in natural man-made systems is constantly changing. Every inch every minute it is different--sometimes minutely, sometimes radically. water coming out of properly designed storage can be of significantly higher quality than water that goes into it. Conversely, poorly designed storage can degrade water quality. Changes in water quality can be physical /or biological, intentional or unintentional. Intentional changes are accompanied by unintentional consequences. ( example, chlorination of water containing organic matter results in formation of toxic trihalomethanes.) Some of these changes don't matter; some do. purpose of this section is to equip you to make sure quality of your water improves in storage. We're going to look at: ways to improve water quality in storage hazardous disinfection byproducts effects of heating bacterial regrowth problem of leaching water age how to test stored water (There is more information on water quality under Materials, p. 39, Emergency Storage, p. 75-76.) Ways to Improve Water Quality in Storage Attrition in well-designed container reduces harmful pathogens; they die off faster than they multiply. This is because human pathogens are designed to thrive in human body, not cold, nearly nutrient-free, dark water tank. longer water is stored less favorable survival conditions, more attrition occurs. Settling in still tank can reduce amount of suspended solids (turbidity) in water. Materials denser than water sink; materials less dense than water float. Settling hours or days is highly effective, low-maintenance form of filtration. This is (in part) how septic tank turns chunky raw sewage into clarified septic effluent--water that you can often see right through. This same principle works on drinking water in tank; it can turn it from clear to really clear. Bacteria in water can Ïride" in suspended solids, so settling can also reduce amount of bacteria in water column. more still water longer it sits, more settling. smallest, most neutrally buoyant particles will never settle. jiggling of water molecules themselves keeps them aloft. Deflocculation speeds settling. Treatment plants add coagulant such as alum to make particles clump together settle. This is beyond scope of most small water systems. Pasteurization will kill most pathogens; example, by heating drinking water to 149ÍF (65êC) five minutes. Ozonation kills pathogens by oxidizing them hyper-reactive, unstable molecules consisting of three oxygen atoms together instead of usual two. adequately sized tank is key element treatment ozone. tank full of water saturated dissolved ozone can handle spikes in amount of incoming debris /or pathogens, whereas low, steady output of ozonator by itself could easily be overwhelmed. (See Ozonators, p. 71.) Ultraviolet light kills pathogens by frying them high-energy light waves just above visible spectrum. Normally UV light goes in pipe rather than tank, to ensure that all water is illuminated. Chlorination kills pathogens. Unlike ozone, UV, or heat, chlorine has long-lasting residual that continues killing microorganisms long after it has been added. example, chlorine added at tank can be effective all way from tank, through distribution system, to tap. Aeration causes some chemical contaminants to oxidize to less noxious forms, while it causes others (such as chlorine some aromatic hydrocarbons) to evaporate. It also discourages anaerobic bacteria. Aeration can be accomplished simply by using inlet aerator (p. 67). Hazardous Disinfection By-products Disinfection chlorine produces toxic, unintentional byproducts it reacts organic matter in water. These include carcinogenic trihalomethanes. Chlorinated drinking water causes at least 4,200 cases of bladder cancer 6,500 cases of rectal cancer year in U.S.5 If at all possible, it is better to avoid use of chlorine. Ozone is used in Europe, example. If use of chlorine is unavoidable, filter suspended solids from water first, use as little chlorine as possible. Effects of Heating Heating water causes physical chemical changes, some of linger after water has cooled: Reduction in amount of dissolved gasses, most significantly oxygen. Gasses are driven out of water by heating. Those little bubbles that form on bottom of pot long before water boils are not steam; they are dissolved air being driven out of solution. Water saturated dissolved air tastes better, is better irrigating plants. Precipitation of calcium carbonate: On heating, calcium can precipitate out of solution, potentially clogging pipes boilers. Pasteurization eliminates pathogens. Bacterial Regrowth Without disinfection (or sometimes it), there can be vigorous growth of microorganisms on inside surfaces of water infrastructure. There are numerous studies on this phenomenon,6 but they skim over most important question: Are these bacteria health problem? impression get is that people who manage study water systems are offended by idea of bacteria in their system, whether or not they are hazardous. most damning indictment of bacterial regrowth seems to be that their colonies could offer shelter to other, actually harmful organisms if they found their way into system. Bacterial regrowth on its own does not appear to be health issue. Water bottles that are reused over over without washing develop vigorous bacterial growth, to point that it can be seen smelled, but there doesn't seem to be any indication that this is anything other than aesthetic issue. (Studies have shown serious problems household water containers in village settings, but problem is not bacterial regrowth from clean water; it is unwashed hands introducing fecal matter into water containers.) Problem of Leaching Natural rocks, plumbing, tanks--every material that touches your water leaches (dissolves) into it to some degree. Is it OK to drink water that has been sitting in plastic? Is it OK to drink water from new concrete tank? These aren't questions simple answers, especially you reduce them to practice--you've got to contain your water in something, after all. There is extensive collection of information on this topic in our Water Storage Extras,6 including summaries links to dozens of studies that relate to leaching permeation of toxins (as well as disinfection byproducts, water quality standards, bacterial regrowth in water systems). At risk of oversimplifying, here is summary. Leaching is of greater concern : materials of greater toxicity materials dissolve more readily longer contact time higher temperature softer water (particularly if it is less than 100 ppm total dissolved solids, as rain is) more corrosive water (containing salt, hydrogen sulfide, etc.) water of extreme pH, especially low pH, acidic water hazard of leaching can be reduced in these ways: Seek water source that is clean to begin . Clean storage isn't going to help toxic water. Water providers have to publish EPA-mandated Ïconsumer confidence report" describes system's water quality. If you have your own system, consider doing your own testing. Bottled water companies are actually subject to less regulation. Natural Resources Defense Council did survey of bottled waters found one particularly egregious offender was private-labeling Ïspring water" from well in industrial parking lot over toxic waste dump!7 Keep your water cool. colder your water, less of your plumbing will dissolve into it. Cold also retards bacterial regrowth. Painting your tank light color /or placing it in shade to lower its temperature is always good idea. Minimize contact time surface area. leaching of plumbing materials often proceeds so slowly that reducing contact time surface area can significantly reduce amount of undesirable materials leached into water. Make sure your storage is plumbed so that water circulates through whole water column, rather than leaving big Ïdead" zones. Raise pH of your water by adding lime. Use materials of minimum toxicity or solubility. (There is overview of toxicity of specific materials in Table 7, p. 40, followed by details on specific materials.) Water Age There are water quality problems that can be caused or made worse by water spending long time in your system. These include: temperature increase taste, odor, or color changes decay of disinfectants formation of disinfectant byproducts bacterial regrowth/ shielding of pathogens It is preferable to design your system so that there are no stagnant backwaters water never turns over. In tank, inlet should be opposite outlet. Abandoned runs of pipe should be capped at beginning, not end. Generally, water age is not problem in well-designed small systems if input water is of good quality. most common exception is rainwater harvesting or other systems that collect water high load of organic matter, traces of bird feces, etc. You don't want to collect this untreated water in black tank in full sun leave it to fester all summer. How to Test Stored Water You can tell lot about quality of stored water by: Tasting or smelling it, can reveal problems over-chlorination, septic conditions, sulfur, iron, hardness, pH, some types of leaching from plastic containers. Holding it up to light (or looking through it), can reveal amount nature of suspended solids (turbidity), , properly illuminated, look like dust swirling in shaft of light. Unfortunately, you can't establish that water is pathogen- or toxic chemical-free by these means. conventional way to test water pathogens is to do few precise, expensive tests indicator bacteria such as general fecal coliforms, using certified lab. However, this often does not yield accurate picture because it is too expensive to do enough tests this way to see how quality changes as it moves through system or over time. In our Water Quality Testing download,4 describe technique doing your own general fecal coliform bacteria tests using materials cost under two dollars per test. results aren't very precise, but you can afford to take enough samples to see how quality changes over short distances timespans, all throughout your system. As Natural Building expert Ianto Evans says: ÏBetter roughly right than precisely wrong." To test contamination pesticides industrial chemicals, there isn't any alternative to sending your water to lab.8 If you live down current from agriculture or industry, this isn't bad idea. Chapter 2: Ways to Store Water We're going to take in-depth look at water tanks in Chapters 3-5, but that doesn't mean tanks are your only--or best--storage method. Some methods will apply in given situation while others won't. To decide on water storage method (or methods), evaluate each option below your context: Source direct (no storage)-- rarely applicable but desirable option if you have clean source higher in elevation flow than water uses. Store water in soil--inexpensive supplemental irrigation storage in soil (not advisable in landslide areas). Store water in aquifers--free bulk storage safe from evaporative loss, but only accessible by pump subject to contamination extraction by other users. Store water in ponds--inexpensive bulk storage of water, most appropriate rainfall exceeds evaporation majority of water need is non-potable uses. Store water in tanks--most expensive but most flexibility in location best protection control of stored water. We'll consider each of these options in turn. Once you've established storage option(s) apply you, you can skim or skip sections apply only to other methods. (You can also, of course, store water in miscellaneous containers, such as drums or recycled milk jugs. See Emergency Storage p. 75, Really Cheap Storage, p. 50.) Source Direct (No Storage) If flow of water source is equal to or greater than peak demand, if it is clean, reliable, above point of use, you don't need artificial storage. You can use natural storage in earth that feeds your spring or creek. town of Stinson Beach, just north of San Francisco, has nearly thousand people on Ïcreek direct" system. Thanks to abundant natural storage relative to its population, this is one of California communities least affected by drought. Source direct is simplest approach to storage; there's not lot more to say about it other than what you can see in figures below under Examples/Creek Direct, p. 85. latter example features tiny Ïdemand-side" storage tank days creek is turbid to blast air out of lines after servicing. Store Water in Soil Storing water in soil isn't going to address anything other than irrigation needs. But irrigation, look first to soil to store water, only after this has made its optimal contribution make up difference other, more elaborate water storage options. Think like water moment. Visualize rain, falling on earth. does it go? water from very short, light rainfall will re-evaporate from surface, none of it cycling through plant roots. more sustained rainfall will start to fill space between soil particles. Plants can absorb this Ïfield moisture" their root hairs pump it out through their leaves. sustained, penetrating rain will fill all space between soil particles to Ïfield capacity," at point water will start moving downward. If it goes below root depth, it will continue on down to groundwater (covered in next section). variable portion of rainfall will also run off over surface, but that is another story. In fact, this whole process is another story, is covered in detail in our forthcoming book Rainwater Harvesting Runoff Management.3 Our concern moment is water held as film over soil particles, within root reach of surface. While level of aquifer rises up down, soil moisture makes thinner or thicker film of moisture over soil particles. space between particles isn't saturated, it's like sponge that is not dripping. water won't flow can't be drawn out pump; it will only come out via root hairs, or slow diffusion of water as gas to surface. Water stored in soil differs from storage in aquifers in several important ways: Table 2: How Storage in Soil Differs from Storage in Aquifers Soil Aquifers Water is generally suited Irrigation only All purposes Water can be extracted by well or spring No or intermittently Yes Water can be extracted by plant roots Yes Only if shallow Space between soil particles is saturated water Briefly Yes Water movement (in both soil aquifers flow is usually only inch to few feet day) Towards drier soil as gas or by capillary action, downwards, by bulk flow By bulk flow, mostly lateral, seeking its level Water has distinct level No Yes Water has been purified of nutrients pathogens by bacteria roots Not yet Yes (unless natural purification capacity is exceeded) typical way to take advantage of ability to store water in soil in excess of current plant needs is to infiltrate rain or other excess water into surface plants are growing, minimal or no runoff. There are range of measures that can be employed to accomplish this, all covered in Rainwater Harvesting Runoff Management. Soil can hold on order of extra gallon of stored water per cubic footm, between wilt point field capacity ( point at leaves of given plant will wilt lack of water, water holding capacity above water starts to flow out of soil like drips out bottom of saturated sponge). Water in soil in excess of plants' current water needs, but less than field capacity, will sit there until plants need it. You can reduce Ïleakage" (evaporation) out of surface of soil by mulching, or by breaking up surface hoe or plow. This breaks capillary connection to stored water, preventing it from evaporating. In our tiny quarter-acre (1000 m2), we can absorb 50,000 gal (200 m3) of runoff diverted from area above our land in one big storm. water is filled bacteria, storage leaks out bottom, evaporates out top, only fraction of this may end up being accessed by our orchard useful irrigation--but so what? Storing water this way is literally dirt-cheap. modifications to our greywater system to funnel water to soil cost less than $50, or about one-thousandth cost of tank of similar capacity. ( same end can be accomplished zero materials cost--nothing more than furrows dug in earth.) In any case, captured runoff serves to flush salts below root zone. In our orchard, water stored in soil shortens our irrigation season by two or three weeks on each end, reduces tank size we need considerably. What's more, water that leaks below root reach ends up stored in underground aquifer, from (since our geology is favorable) we can pump it back up use during dry season. Conventional management would be to shed all this excess water, then import it from somewhere else it is needed. There are rational reasons to shed runoff this way: Some plants can get root rot if soil is too waterlogged too long. On steep slope or unstable soil you may wind up causing your house to slide down hill or into quicksand. Pay close attention to your context, however, you can reap benefit from this storage secondary benefits of reduced flooding improved natural water quality. In rare instances, soil storage can serve much more. example, waterfall filling pool diversion shown on p. 25 is formed entirely from water held in soil sponge of small forested watershed at top of it. This isn't aquifer--it drains rapidly after each rain. It supplies all water, seasonal hydropower, community of dozen or so homes. (This system, includes dozens of tanks of every description six months each year of zero water income, is profiled on p. 83 on our website--search ÏHuehuecoyotl.") Store Water in Aquifers aquifer is underground reservoir of groundwater. Water in aquifer saturates all space between particles. This saturated zone has definite level, like underground lake or river. You can get water out of aquifer well, or, if you're so lucky, spring above your house, artesian well, or horizontal well. Water flows out by itself from these latter two as if they were springs. (See Figure 6, p. 18.) How Water Gets into Moves through Aquifers Because no one ever sees aquifer, most people have hard time visualizing what one looks like how water flows through it. You, however, will shortly have above-average understanding of aquifers÷ good example to start is aquifer under Maruata, Mexican village 've worked several years. Maruata is located in wide valley, bottom filled sand (see photo diagram, next page). it rains, rain filters down through sand until it hits bedrock below. Picture kids' sandbox, sand slightly sloped, one side open. Make rain by putting sprinkler on so sand is getting wet. Now make highland spring, by putting hose on trickle at upper edge of sand box. water will sink into sand. It will flow slowly under surface, around particles until it hits impermeable floor, at point it will creep towards open end. Underground, water moves so much more slowly that it backs up spreads out. It is more like barely moving underground lake than underground river. If you were to dig down into sand, you would find standing water. This is aquifer, you've just made well! If sprinkler (rain) is coming down really hard, water may run over surface before it all sinks in. Some of it might carry leaves debris from surface into well, contaminating groundwater. This happens in Maruata during monsoon. floor three sides of sandbox are waterproof, like bedrock surrounding Maruata's aquifer, while down slope side is open sand bank. Maruata's groundwater/ underground river seeps out through underwater sand bank into ocean at mouth of valley. If burrow my feet down into sand while bodysurfing, can feel cooler, fresh underground river water flowing out of sand into salt water. If dig big hole in wet sand during falling tide test water at bottom of hole, it will be mostly fresh. If flow of underground river is low, dig during rising tide, water in hole will be ocean water sloshing up into aquifer. If sandbox sprinkler is on long enough, groundwater level will rise until it reaches surface, then run over it. In Maruata, river runs over surface much of year. Suppose you were to put sump pump in your sandbox well turn it on. water level would drop rapidly, water would start flowing towards pump from all directions, including reverse flow from ocean towards well. After few minutes, Ïriver" on surface would diminish, then go dry near well, then along its whole length. If there were ocean at mouth of your sandbox, within short time you'd have exhausted fresh water you'd be sucking salt water into your well. If you spray insecticide over surface, sprinkler will carry it down into sandbox aquifer, within minutes it will be coming out of your well. Ditto if you were to inject sewage below purifying reach of plant roots. Figure 5 shows how various activities on surface impact Maruata's aquifer. ( more on how application depth location impacts treatment, see our other publications.9) Aquifers get more complicated you add impermeable (or Ïconfining") layers (see Figure 6). In this case, water that seeps into ground you live may not end up in groundwater directly below you. In fact, surface that recharges your groundwater may be long distance away, may not correspond to surface watershed at all. If your geology contains impermeable layer, you may have Ïperched" aquifer on top of it. aquifer is sandwiched between confining layers both above below, it can be artesian. artesian well is pressurized. If you drill through confining layer into subartesian aquifer, water will rise partway up shaft by itself. In artesian well, aquifer is under enough pressure to rise up shaft all way, flow out surface. How to Increase Amount of Water in Your Aquifer To increase amount of water in your aquifer: take less water out of it increase rainfall infiltration coefficient ( percentage of rain soaks in) detain water in infiltration basins infiltrate water through creek beds riverbeds inject water into wells Not to belabor obvious, but conserving water is cheapest, simplest, lowest-impact way to relieve water shortage, above or below ground. If you have excess water, you can get it into storage in ground using strategies above. (See Runoff Harvesting Ponds, p. 21, some info Rainwater Harvesting Runoff Management3 much more on this topic.) Conjunctive Use ÏConjunctive use" is fancy name adding to groundwater storage you've got more water than you need (by surface infiltration or injection well), then taking it out you need it. This can mean adding water during wet season use in dry season, or adding water during wet decades use during drought decades. Conjunctive use is excellent, so long as it doesn't degenerate into next practice÷ Overdrafting, Mining Fossil Groundwater Overdrafting groundwater is just like overdrafting your checking account--taking it out faster than it is replenished. result is water bankruptcy. After years or decades of excess, at some point you reach bottom. Or, you drill so deep water is unusably hot, nasty, salty from water-rock interactions at depth--almost as if drill were getting too close to Hell. Much of world's accessible groundwater is in state of overdraft. Overdrafting can cause permanent damage to aquifer, subsidence of land, sinkholes, salt water intrusion from ocean. overdrafting, best-case scenario is that you are stuck using amount of water that corresponds to natural recharge, as you should have done in first place. difference is that you may be paying several times more to pump it from much further down, possibly hundreds of feet further down. Worse, you won't have that nice cushion of ten, hundred, or thousand years' past recharge in bank conjunctive use. worst-case scenario is that you were mining fossil groundwater. Fossil groundwater infiltrated into earth in distant past, climate surface conditions were different, like Sahara was dinosaur-filled swamp. current conditions on surface, it may not recharge even in million years. mining nonrenewable fossil water--as extreme overdraft--natural recharge may be so much less than what users have gotten used to consuming that they may have to abandon majority of their farmland, housing, or industry to adjust to new water budget, even state-of- -art water efficiency. Protecting Groundwater Quality While tanks can be managed individually, quality quantity of water in aquifers depend on wider community. Water stored in aquifers can be threatened by toxics from underground gasoline storage tanks, dry cleaners, agricultural poisons, nitrates--all dreck of modern life seeps down through soil. best defense, of course, is to avoid such contamination in first place. Unfortunately (or fortunately), this requires complete rethinking of almost every aspect of our material life. While soil is formidable treatment engine biological pathogens nutrients, it is relatively transparent to artificial toxins. Toxic contamination of groundwater is increasingly widespread. Would you drink out of parking lot gutter? If it drains into your groundwater, you are doing so already. only reason water isn't more gross is that modern toxins introduced decades ago are just now reaching aquifers. It doesn't seem that any amount of effort can truly rehabilitate aquifer that has been contaminated by nastier substances. Fortunately, nitrate, is most common groundwater contaminant, is relatively easy to flush out if source is removed. Salt water intrusion is another class of threat to avoid. It is caused by overpumping, so that groundwater level drops below that of ocean. remedy: Pump less. Store Water in Ponds pond is artificially constructed, open-surface body of water that is supported structurally by earth, filled by runoff, underlying springs, /or water diverted into it from elsewhere. Ponds are generally large in capacity relative to flow of water that maintains them. Ponds or aquifers-- is better bulk storage of excess water? Imagine setting open-topped drum in your yard. Will it eventually fill to overflowing? If so, your climate has more rain than wind sun. climatologist would say your precipitation exceeds evapotranspiration. If this is case, then ponds are appropriate choice water storage. If, on other hand, drum would never fill, then it is better to store water underground it is protected from evaporation (see Evaporation, p. 23, figures). Ponds offer lot of water storage low price. On downside, they are wide open to contamination; they may lose quite lot of water to evaporation, may leak out bottom as well--especially new, unlined ponds. Water stored in ponds is typically of lower quality than water stored in tank not suited drinking unless treated. What's difference between ponds dams? dam is impoundment astride year-round watercourse, whereas pond is located it intercepts only runoff, or is totally separated from surface water flows--its own little watershed. Dams, particularly large ones, have serious environmental consequences. Even small dam can create barrier that isolates populations of fish interrupts migrations of salmon or steelhead trout. large reservoir of slack water behind dam changes temperature sediment flow of stream, adverse consequences. Pooled water behind dam is rapidly lost to evaporation. Since all dams fill to rim sediment within few decades to at most several centuries, they fail any test of sustainability. We've turned corner on dams in U.S.: rate of dam removal now exceeds rate of new dam construction. If you want to extract water or power from stream or river, use diversion, rather than dam. Properly conceived ponds, on other hand, offer prospect of positive environmental as well as human benefits, including: water storage, primarily irrigation, livestock watering, fire safety conversion of runoff to groundwater recharge or surface water that is available in dry times place to swim, ice-skate, fish, view wildlife aquaculture, generally of fish aesthetic beauty microclimate modification (reflect low winter sun, place to cool off in summer) wildlife habitat birds, aquatic creatures, plants drinking water source hunting area bigger creatures Constructing pond is major undertaking. Start visits to nearby ponds questions to their owners. In many areas, government agencies such as your county's Soil Water Conservation District, U.S. Department of Agriculture Natural Resource Conservation Service, or University Extension will help you design your pond free.10 It is safest to retain services of someone who knows what they are doing, good local track record, to help situate, design, build pond. There is increasing interest in pond safety. Many states are conducting routine checks of ponds dams, condemning those deemed unsafe. Construct your pond well, you'll avoid expensive repair or liability from downstream neighbors. design of pond depends on its use. Before moving earth, get clear on why you want pond what you'll use it . Ontario, Canada, Land Owner Resource Center cautions against over-ambition: ÏMulti-purpose ponds seldom fulfill all of their intended uses.11" Once you know size of pond it will be located, amount of earthwork materials costs can be estimated. Types of Man-Made Ponds to Put Them Man-made ponds have several major design variables. These yield three main classes of ponds, we'll call Storage Ponds, Living Ponds, Runoff Harvesting Ponds (see Table 3, next page). Storage ponds are essentially open, earth-supported tanks. These should be situated well out of flood plains, , highest water quality, should have raised rim whole way around them so that little or no uncontrolled runoff enters them. Living ponds may look just like natural ponds. They should be located out of flood plains. Sometimes they have provision routing runoff into them or diverting it at will. Runoff harvesting ponds are seasonal ponds that collect runoff that would otherwise be lost allow it to infiltrate slowly into soil--like big, slow-draining infiltration basin. At their simplest, they are formed by making low dams across runoff courses. This type of pond is covered in more detail in our forthcoming book Rainwater Harvesting Runoff Management.3 Construction techniques go hand-in-hand pond location: Excavation ponds are made by digging in flat land piling earth into levees around hole. In areas high groundwater, hole may fill water by itself, in case impermeable bottom is not required. Embankment ponds are formed by making levee between two hillsides. Don't build this kind of pond astride permanent watercourse or large-volume runoff channel, as likelihood of ecological damage failure is too high. Combination ponds are made by combination of above two techniques .e., cut fill. Flat sites are generally considered easiest pond construction. However, natural folds in land can Ïhold" pond in pleasing way, possibly reduce amount of costly re-arranging of soil. pond needs to be built there is access heavy machinery. Native soil that holds water is clearly positive site attribute pond. Fissured bedrock may drain pond. Maintaining pond in swampy area may be expensive problematic. Clearly, it is advantageous to situate your pond such that it can fill by gravity from water source. Vegetation around pond site will reduce erosion improve water quality. Convenient access privacy are other considerations. Pond Water Sources source requirements vary by pond type: Storage ponds require water source of quality commensurate end use, just like tank, but bit of extra quantity to compensate evaporation. Living ponds require water of quality that will support aquatic life, in quantity that can maintain pond level constant year round, despite evaporation, leakage out bottom, any extraction of water other uses. Living ponds are often maintained by diversion from natural surface watercourse, provision blocking entry of storm water sediment. Runoff harvesting ponds at their simplest are formed by making low levees across runoff courses. Quality generally isn't issue. quantity shouldn't blow out dam. You don't want too much water. Flooding causes problems in sport-fishing ponds, in particular. It is good to be able to control entry of water, sediment, nuisance fish into pond screen /or valves. aquaculture, water should be tested. Runoff can contain agricultural chemicals; groundwater can contain nitrate or carbon dioxide. Groundwater from springs or runoff from naturally forested areas are superior water sources. In areas ponds are common, you can probably find locally known formula how much area of watershed it takes to keep pond of given volume full. example, in Virginia, it takes about three acres of watershed to maintain acre-foot of pond volume, more if watershed is forested sandy soil, less if it is pasture or clay soil.m, 12 Evaporation How much water will evaporate? That depends on surface area, heat, humidity, wind. These values can often be found nearby weather station, as well as direct evaporation figures. Evaporation values dry month vary from few inches in temperate climates to half dozen in full desert conditions.13 even modest pond, amount of evaporative water loss is considerable. example, quarter-acre pond evaporates about four inches of water in average dry month. That equals water loss of 26,000 gallons. Average evaporation from 3000 acre surface of Lake Cachuma, reservoir above Santa Barbara, California, exceeds 10,000 gallons per minute, every minute of year-- powerful reminder that in arid zones it is preferable to store water underground.m Pond Size To save on construction costs, maintenance effort, environmental impacts, pond should be no bigger than necessary your intended use. Smaller ponds have fewer problems wind wave erosion on banks. Bigger ponds store more water at lower unit cost. Storage ponds can be sized like tanks (see p. 32). Living ponds should be no bigger than water source can comfortably support. sport fishing, ponds should be one acre or bigger (4000 m2), to provide sufficient cover food population of fish that can't easily be depleted. Runoff harvesting ponds are usually sized to topography ease of construction. upper size limit is size at they can contain all runoff they are likely to encounter. Pond Depth Ideal pond depth is function of intended use weather conditions. water storage, deeper is better. Ponds should be at least 12 feet (3.5 m) deep, up to maximum of about 20 feet (6 m). living ponds, depth should be between 8 15 feet (2.5-4.5 m) in 25% of their basin. colder climate, deeper pond, up to maximum of about 15 feet (4.5 m). Beyond this depth, there may be deep zone without oxygen, can mix upper layers kill fish if pond Ïturns over", .e., water layers swap position due to change in relative temperature. Runoff harvesting ponds are typically shallow-- few to 5 or 6 feet deep (0.75-2 m). If they are in watercourses, high walls risk of catastrophic failure is too great. Pond Shape While round is most efficient pond shape, natural shape is most pleasing. kidney shape is popular compromise. Deep water along shore discourages weeds. inside walls of pond should slope about 1:2, outside of walls 1:2 or 1:3. Pond Inlets Outlets pond should have: permanent drain capable of draining pond in five days or less. controllable inlet to exclude floodwaters, sediment, unwanted fish. fence to exclude livestock from pond (they'll make mess of water). Instead, provide watering trough outside fence supplied by pond. well-armored overflow, generously sized so that overflow goes through it rather than over unprotected face of levee. Overflows are often cut into undisturbed native soil beyond sides of levee. If overflow goes over fill soil of levee, it should be well-armored against erosion. Ponds placed in natural runoff courses must be designed to withstand floodwaters. Pond Liners Ponds may be lined native clay soil, sandy soil sealed bentonite clay, or welded liner of EPDM at least 2 mm thick. Rubber liners should be covered at least six inches (15 cm) of sand or fine soil to protect them from punctures (although water storage ponds are not used any other purpose often have just naked liner). Levee Construction levee (wall) contains pond water. building levee, as pond construction in general, you should retain services of expert. We caution on environmental grounds against damming year-round watercourse. These type of ponds often fail structurally--another reason to make Ïexcavation" ponds instead, soil is removed piled up to make levees outside of watercourse. It is not advisable to make levee higher than twenty feet (6 m). Once you know size of pond it is going, amount of earthwork materials costs can be estimated. site must be cleared of vegetation topsoil, excavation marked stakes. joint between levee native soil is weak spot, should be armored against leakage clay core (see Figure 8, next page). After filling core trench clay, drain line ( anti-seep collars) can be installed. levee is constructed in thin lifts of well-compacted clay soil, needs to be wide enough at top that creatures such as muskrats can't bore extra outlets through it. spillway is floodwaters that exceed capacity of overflow can escape. It is most likely point of failure on pond. It should be sized generously, if possible be situated in undisturbed soil to side of levee, instead of pouring down face of it. In latter case, armor it against erosion. Virginia Extension12 uses this formula to size spillways: Add 15 feet to half of watershed area in acres. example, fifty-acre watershed should have forty feet of spillway, 200 acres 115 feet. This should result in overflows less than foot high, will reduce loss of sport fish reduce forces on spillway.m sides of levee can be armored rock riprap against wave action. Wildlife Ponds pond will always attract wildlife. If you want to attract more critters, or specific species, you can attract them habitat variety of fruit-bearing plants. shallower, irregular shoreline varied cover open exposures will attract more creatures, as will nesting boxes. Sport Fish in Ponds Water characteristics must be right particular species of fish to thrive:13 Water temperature is critical. Cold water fish, such as trout, require surface water temperatures of 60-70êF (15-20êC). Cool water fish such as smallmouth bass, pike, rock bass can tolerate temperatures of 70-80êF (20-26êC). If you expect higher temperatures, stock warm water fish such as catfish, bluegill, largemouth bass, can tolerate temperatures of 90êF (32êC). pH should be between 5 10. To raise pH, powdered lime can be added. Dissolved oxygen is crucial fish. Most of oxygen in ponds comes from photosynthesis by water plants. There should be enough water plants to generate oxygen during day, but not so much rotting, matted algae root tangles that oxygen is consumed overnight. Oxygen levels of 5-6 ppm are required fish to thrive. Water clarity helps sport fish. clear pond will support significantly more of them than muddy pond. Livestock cause all kinds of water quality problems should be fenced out of sport-fishing ponds. Pond Maintenance Levees must be protected from tunneling digging of crayfish, muskrats, beavers, nuisance fish. Aquatic weeds may need to be controlled--this can often be accomplished by lowering water level removing weakened or killed plants. pond may periodically need to be dredged. Any gullies that form in levees must be filled. Woody plants on levee must be controlled by mowing, as their roots can create leaks in levee, attract burrowing animals that make more leaks. Store Water in Open Tanks, Swimming Pools Rather than roof screen their water storage, some people prefer their cisterns au naturel. big advantages to this approach are that you avoid cost of roof, ... you can swim in it! Toss in some Gambusia (mosquito fish) to eat mosquito larvae (but keep them out of natural waters). Either live algae or put some vascular plants in system to pump nutrients out of solution (they out-compete algae nutrients). If you've got flow, you can use it to create Ïskimmer" effect to clean off leaves dust. Natural pools, are filtered purified biologically instead of chlorine, are possible but beyond scope of this book, as they're not primarily water storage.14 If you want to be able to dunk without all these complications, you can put removable lid on small water tank. 've done this 900 gal redwood tank, it worked great (photo, inside back cover). Above-ground swimming pools are cheapest, funkiest storage going. Not long-term solution, but you can't beat cost. (See Really Cheap Storage, p. 50.) It is intriguing design challenge to create more or less standard concrete swimming pool functional cover, filtration, skimming, to be usable both storage swimming--all at widely varying water levels. It appears that level change of perhaps 14" (35 cm) is possible within these constraints. idea is that pool can be topped off rainwater during rainy season, then level allowed to fall as water evaporates during dry season so water doesn't have to be added to pool. At minimum, pool should have built-in steps, be designed so it is not drowning or falling hazard. Unlike regular swimming pool, Ïpebble tech" pool ( exposed aggregate on inside) won't crack if left dry. (If you figure out more about how--or how not--to do this, please let me know.) Store Water in Tanks Tanks are most common way to store water. well-designed tank offers nearly complete control of storage conditions, including: security against leakage protection from mosquitoes vermin shade so algae will not grow minimal or no evaporation valve-controlled inlets outlets We'll now spend next three chapters looking at water tanks in detail.Chapter 3: Water Tank Design As we zoom in to focus on design of tanks, then plumbing details, remember to look up once in while at global view of your system its context (Chapter 1). In this chapter we'll be looking at: overview of tank components situating water tanks sizing water tanks tank shape tank materials tank footings floors tank roofs tank costs regulatory requirements hazards of stored water water tanks special applications Tank Components Overview Most tanks will have: inlet outlet service access drain overflow mechanism critter-proofing air venting provision sunscreen We'll look at these components in detail in Chapter 4. Water tanks also can have host of optional features, we explore in Chapter 5. All these valves, fittings, doodads together add up to quite list. design water system, list every significant component in table. each component, table describes component's: function in system generic name size material states in different system modes (dry season, wet season, fire emergency, supply interruption, maintenance) how to replace it what to replace it it fails example: Component Type Size Material State in system modes Replace Tank drain valve Ball valve 2" Brass Open tank cleaning after tank is drained as far as possible through outlet. On onset of leaking remove reduction replace 3" brass ball valve. It's better to get handle on system's complexity to work out design issues on paper--rather than saw or jackhammer. You can see more of this table on p. 84. Situating Water Tanks location of your water tank will largely determine: parts of your land can be supplied tank water by gravity amount of pressure at every point in system length cost of pipe runs, control wire runs, line-of-sight radio links how visually obtrusive your tank will be vulnerability of tank pipes to hazards such as falling trees, rocks, landslides size of tank it is feasible to build ease of construction service access To situate water tank, you need to consider: elevation stability of soil slope aesthetics, sacred spots security Elevation If you have hill, put tank at elevation on it that yields adequate pressure.m In places there is no hill handy, you can: make water tower (to artificially increase elevation) use small pressure tank (to pressurize water as it is needed-- have no water power goes out) use huge pressure tank (to store pressurized water at low elevation) put tank on your roof ( live low pressure, like most people worldwide) Pressurized from roof height, your appliances will barely work. your tank equivalent of ten stories above you, your washing machine, reverse osmosis water purifier, demand water heater will start to work. your storage 23 stories up, your fire hose will work optimally. tank higher than 23 stories, things will start to blow up. maximum advisable pressure conventional plumbing is 100 psi. You can always install regulator to lower pressure to whatever value you want. If water can make it into your tank by gravity flow, only reason to limit its elevation is have shorter pipe run from storage to use, can improve water security lower cost. hydroelectric power, there is no maximum pressure-- more better, period. However, most hydroelectric systems should be plumbed directly to source, no tank (except possibly settling tank) in line. If you are so lucky as to have hydroelectric source high, high above your home, you can put hydroelectric generator before your tank, so that you extract extra energy before storing water well above your home. If flow is sufficient pressure is not, option is to have hydroelectric outlet be headwaters of fountain just below your home. What is minimum elevation your water tank? In terms of resource conservation, lower pressure better. Outside of industrialized nations, very low water pressure is norm; it works fine. If only thing you need lots of pressure is fire safety (possibly legal requirement), it may be economical to install booster pump or separate, higher tank just firefighting. higher you have to pump water to your tank, higher your lifetime electric bill environmental impact will be. Table 4 (below) shows minimum maximum pressures several applications: Tubs kitchen sinks need flow, not pressure. If your pressure is very low, you can use larger-diameter pipe to get acceptable flow. (Figure 31, p. 87, shows kitchen sink almost zero pressure.) Stability of Soil Slope You don't want your tank to sink into ground, or slide down hill. load per unit of area from water tanks is actually quite low.m person walking can easily place much higher point loads on soil. On other hand, no one has feet as big as water tank. It's aggregate load from water tank--all that area being pushed on at same time--that can push your building pad down into gully. However, undisturbed native soil is sufficiently strong to support even large tanks. In case of tank on slope, you don't have natural flat spot, put tank on cut (newly exposed, undisturbed soil), rather than fill (freshly dumped, loose soil). really large tank or any tank on fill, it's good idea to consult engineer. (See also Tank Footings, p. 48.) Aesthetics, Sacred Spots Water tanks can be big, although they can be beautiful, they are more often ugly. locating water tank, either: put it it doesn't matter conceal it well make it beautiful Some places are so special that they just shouldn't be built on at all. This is often true of hilltops. Of course, same topography that gives you sunset view of all creation is also advantageous cell phone TV transmitters, (to only slightly lesser degree) water tanks. Unlike transmitters, however, you may be able to move water tank down from hilltop ways to leave silhouette unchanged, without compromising functionality. You may even lower your pumping bill. If you do make tank on tiptop of hill, bury it part or all of way, make it beautiful, ring it trees, /or make it easy to get on top of to hang out admire view. Security Ideally, you want your tank downstream from whatever hazards weak links lie between you your water source. Rivers that flood, gullies that wash out, landslides, falling trees rolling boulders--it's best if as few of these hazards as possible are between you your tank. Buried Storage Burying your water tank has significant advantages over surface storage: less obtrusive cooler totally sun-screened more secure against accidental drainage considerable frost protection ... some real disadvantages: except on steep hill, you can't install gravity drain, so tank is difficult to clean usually requires pump to get water out design is more structurally challenging limits choice of materials to those that don't corrode can be safety hazard water from surface or surrounding soil can leak in contaminate tank inspection, repair replacement are more challenging In my opinion, disadvantages of buried tanks outweigh advantages most applications other than septic tanks. If stored underground, water from source higher than use point often winds up having to be pumped--to use point downhill from source. Pumping water downhill is surprisingly common--one of my pet design peeves. Tanks designed above ground use generally shouldn't be buried. They may collapse under pressure from surrounding soil after while. While all tanks are designed to resist outward water pressure full, tanks burial need special shape construction to resist inward pressure empty. Such pressure can be considerable, especially if soil around tank is wet, contains expansive clay, is subject to frost heave, or is driven on by big trucks. To resist these forces, tanks designed underground use generally: are deeply ribbed shapes or spheres, if made of plastic have thick walls of concrete (any shape) have high-strength walls of fiberglass in cigar shape (like big propane tank) If you expect your buried tank to be empty any regularity or any length of time, it should be designed to resist this inward loading (spherical polyethylene tanks are). Note that deeply ribbed polyethylene septic tanks, though designed burial, are designed to always be full of water in order to push back against soil that is trying to collapse tank. you pump such septic tank, you are supposed to refill it immediately. This style of tank often collapses inward despite being filled water. These are essentially cheap, disposable tanks, installed in location (underground) installation is expensive disposal or replacement is difficult-- bad combination. Wet soil can also pop tank to surface like cork. Tanks are highly buoyant empty. Even something as small as 55 gal drum has 400 lbs of upward force on it empty in wet soil. 1000 gal tank, upward force equals four tons--in right conditions, enough to pop up through asphalt of driveway lift small car.m Sizing Water Tanks size of your storage is one of main factors that will determine under what circumstances you will find yourself short of water, how long. Will demand outstrip supply every morning? there is fire? day after well pump goes out? It will also do lot to determine what your system costs. Sizing your tank is matter of figuring out what degree of water security you want, then finding tank volume that makes most of your water supply within your budget other limiting factors. This is good time to remember reason(s) you want storage, as they will drive calculation of tank size: You want more water security than direct connection to source can provide. yield of source cannot directly provide peak demand. yield of source is less than that required firefighting. source is less secure than water stored in tank (e.g., if source requires pumping water, while water stored in tank doesn't). pipeline distance to source is so far that it is more economical to use smaller size pipe tank, than pipe large enough to carry peak flow all way from source to users.16 biggest variable by far is how much water security you're aiming . In general, more storage you have, better your water security. (See Performance Security Standard, p. 4, discussion of how water security standards tend to get overinflated.) Without storage, security-- percentage of time you've got water--is equal to security of source. more storage you've got, longer interruption to source supply you can cover stored water (see Figure 9, below). Is it possible to have too much storage? Yes. Too much storage can lead to freezing or water age problems (see Water Age, p. 12). More likely, it simply constitutes waste of Earth's valuable resources. Because of high up-front cost of storage, it is rare to see anyone except super-wealthy install too much storage volume. There are factors that can lower optimum amount of storage: Not enough money: Due to high up-front cost of storage, you may wish to live less than optimum amount of storage initially or permanently. Not enough space. Not enough elevation difference: If water source isn't much higher than use location, you may not want to have big tank use up lot of elevation difference ( pressure) between tank's inlet outlet. Problematic access: instance, you may reduce your tank size if you have to hand-carry tank or materials to site. Avoiding waste: Even if you can afford money space, why waste natural resources if more storage doesn't confer much advantage? (See Tunnel Vision, p. 5.) If you hated word problems in math, you may wish to skip ahead to Tank Shape, p. 36÷ Sizing Tank Demand Peaks Exceed Flow Although water needs are usually expressed as value-per-person 24-hour day, in actuality just about all of this water will be used during period of 10 to 12 hours. Over half of entire day's water use may happen between dinner time bedtime, or in morning, depending on culture. Water provided by source during low-demand periods (e.g., overnight) can be stored use during high-demand periods. minimum amount of storage that will not leave you short of water every day usage peaks can be determined by making table comparing water coming into storage compared to water going out, throughout day. If extraordinary demand (e.g., irrigation or weekend workshops) pushes consumption beyond daily production days at time, you may need to look at longer interval. One community, example, has spells of extremely hot dry weather, last up to two weeks. Due to increased irrigation, peak water demand can exceed maximum combined production of all sources several days. 30 houses there is 100,000 gal (380 m3) of storage, is two weeks of average summer use no water production, or enough to cover two weeks of deficit consumption still provide generous fire reserve. Note: most common reason to size storage based on daily demand peaks is that you can't afford enough storage to cover emergencies or supply interruptions. If any of sizing factors below come into play, your system will require more storage volume, daily demand peaks are moot. However, same approach can be used to calculate demand peaks over any other time interval. Sizing Tank You Have Limited Water Supply Scheduled Use This approach is inverse of approach above. It may be appropriate if water supply is limited there are known lengths of time without water use. Instead of sizing tank to cover use, you size tank to cover production of source during longest time without water use. If you store all water that is produced during longest time without usage, you'll have maximized your limited supply. instance, if water use occurs only during day source goes 24 hours day (like spring), or has limited 24-hour production (like low-yield well), then tank should be sized to hold at least night's water production. This way, full 24 hours' production is available during hours of use. bottled water plant in Mexico plans to use water from spring that yields only 2 gpm (4 lpm) in dry season. If plant is idle 16 hours day, full utility of source could be captured 2000 gal (7.6 m3) of storage (16 hours of flow 60 minutes flow per minute). If plant is idle on Sunday, 32 hours of spring flow could be captured Monday's production, using 4000 gal (15 m3) tank. Discretionary tasks that use lot of water could be scheduled Mondays to take advantage of extra water. Sizing Tank to Cover Use During Interruptions in Supply Most systems have at least day's worth of storage to cover supply interruptions due to servicing, fault within system, or disaster such as earthquake or power outage. To size your tank supply interruption, consider what is likely to jeopardize your supply how long (see Figure 9, p. 33). Also consider: If your outlet is at bottom of tank, you may consume all your back-up water before you figure out there's problem. You could install alarm, but mid- low-level outlets valves will provide more security more simply. your taps go dry at mid-level, you can go to tank open lower valve to access your emergency water. (You can also make Variable Height Outlet, p. 68.)Warning: You don't want to have to go open valve to get at fire reserve water. preferred arrangement is to have fire hydrant--only--connected from lower-level outlet than house/ irrigation supply. If you are aware that your water supply is interrupted, you can usually stretch your reserve quite bit longer through conservation. only storage big enough to cover year- or multi-year-long droughts is in natural aquifers (see Conjunctive Use, p. 19), or large open reservoirs ( questionable technology--see dam discussion, p. 20). Sizing Tank Production Is Intermittent If your water production is intermittent ( instance, from harvesting rainwater), your tank should cover maximum cumulative deficit between production consumption. There is simple, graphical technique to calculate this: Plot bar graph of average runoff from your roof by month. Plot cumulative runoff, by adding each monthly figure to all previous ones. Draw line equal to your cumulative water use. Figure 11 (right) shows final graph. gap between cumulative supply cumulative demand shows storage need or deficit. (See Rainwater Harvesting more on sizing tanks rainfall.) Sizing Tank Firefighting If your system is part of project that requires permits, there are likely specific legal requirements system's firefighting capabilities you will have to research fulfill. These probably include much more storage, bigger pipes higher pressure than you could otherwise imagine. residence its own water system may ( example) be required to have: tank 20 feet or more from structure (or fireproofed) 4000 gal of storage, 2000 gal of is set aside firefighting provision supply to automatically start refilling tank level drops below 3500 gal subdivision might require: 6" hydrants 4" 2.5" outlets every 500' enough storage to supply 500 gpm at 100 psi two hours from any of hydrantsm There may be many pages of specifics about every aspect of firefighting water supply in applicable code; be sure to inform yourself about them early in project. Ask your local Fire Marshal to review plans your system provide suggestions. See Systems Firefighting, p. 78, more on water firefighting, including use of foam to enhance utility of small amount of water. Size Structural Integrity As tanks get bigger, structural engineering issues get much bigger. Tanks of thousand gallons are no great challenge. 10,000 gal (40 m3) tank requires serious consideration of loads that will be operating on it. (See Appendix B: Tank Loads Structural Considerations.) Any tank over 30,000 gal (110 m3) should be professionally engineered. tank shape determines how material will resist applied force thus how easy it will be to resist given load. This is something that you should consider carefully if you are making or modifying tank. (See next section Structures Appendix). Tank Shape Now that we've got location size of your tank, let's consider shape. What difference does shape make? Shape affects: how much material it takes to contain given volume of water (materials efficiency) how easily tank material can resist loads applied to it (structural efficiency) how much elevation (pressure) is lost between top of tank bottom how easy tank is to fabricate in given material how easily given volume of water fits into its location See Figure 12: Tank Shapes (facing page) graphical overview of tank shapes. Avoid square or rectangular shapes sharp corners. These are inefficient structurally in use of materials. sphere uses least material to enclose most volume, is most structurally efficient--at least until you try to set it down on flat surface. classic tank shape--cylindrical, about as big around as it is tall, domed roof flat floor--is good combination of structural materials efficiency, ease of fabrication, ease of setting on flat surface. All else being equal, this is way to go. Here are some of exceptions: If you've got very little fall to work , use tank that is wide short so you lose less height between inlet outlet. If tank is pressurized, spheres or cylinders rounded ends (like propane tanks) are most structurally efficient. Location influences shape: Tanks designed to be buried often have special shapes to resist uneven pressure from outside, especially if they are made of plastic (see Buried Storage, p. 31). Tanks on towers, because they don't need to be set on flat earth, can often do approach materials-efficiency ideal of spherical shape (see photos p. iv, 29). Large tanks on steep slopes may need to be made rectangular or oblong to fit ( tank wider across slope narrower in up-down direction, like enclosed, water-holding terrace). In tight quarters, tall cylinders occupy fewer square feet more storage. same can be true buried tanks or squares rectangles, if their shape fits in tighter. cylindrical tanks, diameter equal to height is most materials-efficient ratio. However, it doesn't cost you much extra material to vary this ratio up to 2:1. example, tank 1.5 times as wide as tall only has 2% more surface area than tank height equal to width. tank twice as wide as tall only has 5% more area. Even sphere ( most efficient volume-enclosing shape there is) only has about 13% less surface area per volume than cylindrical tank domed roof. While it may seem that more area equals more material, opposite can be true tanks up to twice as wide as tall. As pressure is proportional to water depth, wider tank, lower pressure given volume of water thinner material whole thing can be made of. (You can use our Tank Calculator to see how this works.)6 exception: As mentioned previously, tanks stiff floors, say concrete slab, need to be thick. Thus, making tank wider takes much more material, since there is more floor wider tank is. Though pressure is less, you still have to make slab thick enough to span twenty or forty feet (6-12 m) without cracking. If you built spherical tank, most of materials savings in reality would be from not having thick slab floor. material your tank is made of makes difference shape, too. factory-made tanks of plastic or steel classic as-wide-as-tall cylindrical tank is most materials- cost-efficient, most available shape. smaller steel tanks, ease of fabricating conical roofs outweighs structural advantages of domed roofs. Circular tanks are difficult to build of rock, especially in small diameters. Rock tanks are easier to build straight walls. shape of best compromise between materials-efficiency ease of construction rock tanks shifts as size increases. square is best up to about ten feet across, then hexagon, then octagon, finally, circle.16 Ferrocement tanks can be just about any shape. If you must have tank in shape of egg, urn, boulder or curled dinosaur, ferrocement is your material. Cylindrical low-domed roof is best compromise between easy-to-build materials-efficient. (See Appendix D: How to Make Ferrocement Tanks.) Tank Materials There are plenty of choices water tank materials, each advantages disadvantages. Table 7 (following page) summarizes their characteristics. Materials Situations to Avoid Despite all contradictory data opinions on topic of how materials can contaminate stored water, few circumstances are unequivocally hazardous to be avoided: PVC exposed to sunlight--PVC breaks down in sunlight, reacting to form carcinogens, leach into water. It is plumbing code violation to have potable water in un-shaded PVC this reason. You can see physical evidence of change on outside of pipe; it darkens, becomes chalky brittle. reaction progresses from outside in. To extent PVC should be used at all, it should be buried or indoors. If you have PVC that has already degraded, you should replace it. Pre-1997 PVC-- was made more toxic plasticizers. Flexible PVC water bed bladders or trash cans-- contain high level of toxic plasticizers. Pre-1980 tank coatings including coal tar lead-based paint--These were great corrosion resistance but oops!--they poison water. Lead pipe pre-1987 lead-soldered copper pipe--Solders flux currently contain less than 2% lead. Before 1987 they typically were half lead. Lead pipe can be recognized by its softness. Western red cedar-- same stuff that smells good keeps it from rotting is toxic ingested. Fly ash in concrete--especially exposed to acidic water. Often worst hazards are not base material, but solvents, additives, mold-release agents, fungicides, etc. more on leaching hazard by material, see summary in Table 7: Tank Materials, p. 40, material by material discussion follows. There are also details on less common plastics in Appendix C, another plethora of information in our Water Storage Extras download.6 NSF International has searchable database of products meet NSF 61, their widely followed standard materials in contact drinking water.20 Glass Glass is unequivocally best material storing drinking water. It imparts neither taste nor toxins, can be washed, heated, reused until broken, at point it can be melted recycled, endlessly, without degradation. weight fragility of glass is issue, but not unmanageable one. In village work in Mexico, villagers are highly attuned to taste quality of drinking water. Five gallon (20 L) glass containers transport storage of drinking water remain popular despite availability greater convenience of plastic. Toxicity/ Leaching: No issue except leaded glass. Taste: Imparts no taste to water. Ferrocement Ferrocement tanks offer nearly durability strength of concrete at fraction of materials use, complete flexibility in shape. They are cost-competitive made to order, or you can make them yourself. Ferrocement is arguably best all-around material permanent water tank. downside? You can't move them. , you will have to make them yourself unless you live near one of few folks who make them to order.21, 22 They are labor-intensive require some construction experience ambition to build. We were unable to find information about resistance of ferrocement to freeze/thaw cycles. (You can see full magnitude of do-it-yourself task in Appendix D: How to Make Ferrocement Tanks.) Ferrocement tanks are constructed from grid of steel reinforcement covered sand/cement mix. resulting wall is only two to four fingers thick, is, particularly if curved, incredibly strong. Toxicity/ Leaching: best protection, use NSF 61 certified cement in construction of your ferrocement tank, NSF 61 certified sealers.20 There is little concern about leaching from cement stucco after it has cured, is mostly achieved within 30 days. exception is acid water or sulfides, could continue to dissolve tank. Taste: May add cement flavor until it is done curing, after there is typically no detectable taste. Galvanized Steel Bolted or welded galvanized steel tanks offer high strength, medium durability, good fire resistance, good transportability, are overall attractive choice. There is substantial range in quality among galvanized steel tanks. thicker metal, better. Corrugation generally indicates thinner metal. Welded steel is more common small tanks. Large tanks can be welded or bolted. Galvanizing works by letting zinc corrode in order to save steel. zinc gets consumed in process. it's used up, steel underneath is left naked unprotected will corrode rapidly. If this is happening in just few exterior spots, you could paint them paint that contains zinc. However, wouldn't trust this stuff on inside of tank containing potable water. As corrosion proceeds, it will result in lots of rusty powder, flakes, sometimes, huge sheets sloughing off inside tank (photo, right). If your tank is displaying this symptom, it would be good idea to add outlet screen. This will keep large pieces of rust from entering plumbing wreaking havoc there. There isn't much else you can do at this point except to save your pennies towards new tank, or consider repair membrane (p. 48). Accounts of short-lived galvanized tanks are generally traceable to mechanical damage to galvanizing, uncontrolled water overflow over outside of tank, lack of firm, free-draining gravel base, or use of electrolytically incompatible copper pipe or fittings. Properly installed, good galvanized tank can last many decades, it's finally done , steel is readily recyclable. Toxicity/ Leaching: Galvanized steel itself may leach both iron zinc into water, but neither of these are great concern humans. Zinc is highly toxic to fish, according to one source. If your tank has liner, then toxicity taste issues will be determined by liner. Taste: Doesn't generally impart taste unless rust is stirred up off bottom, in case water will look taste gross. But since iron oxide is neither particularly toxic nor soluble in water, rust is primarily aesthetic issue. Stainless Steel Cadillac material liquid storage, stainless steel is so expensive it is almost never used water, except transporting it (see Tanks Transporting Water, p. 54). Chlorinated water can corrode stainless steel. Toxicity/ Leaching/ Taste: Stainless steel does not generally leach toxins, nor affect taste of water. Porcelain-Bonded Carbon Steel rarity as water tank material, baked enamel offers strength of steel inertness of porcelain in contact water. 've heard that silo-rings of this material can be salvaged adapted use as water tanks. Toxicity/ Leaching: Generally low, however, some colors contain heavy metals. Taste: No effect on taste. Brass Brass is good plumbing, but rarely used containers, due to its cost. Toxicity/ Leaching: Leaches copper zinc, but does not pose threat to humans. Taste: No effect on taste. Copper Copper is rarely used tanks due to its expense. It is arguably best material rain gutters indoor supply plumbing. Though expensive, it is common in these applications. Acidic water can deteriorate copper pipes. Copper lasts long time. rate of leaching from copper decreases over time, presumably as surface skins over reaction products. Mining copper is environmentally devastating. Copper is readily recyclable. Toxicity/ Leaching: Copper leaches into water enough to kill microorganisms, but is of low toxicity to humans. Taste: No effect on taste. Aluminum Aluminum is rarely used tanks due to its expense, rarely used plumbing due to issues electrolytic corrosion ( plumbing acting like giant battery, metals electrochemically consumed). Absent acidic conditions or electrolytic corrosion, aluminum lasts long time. Aluminum mining is environmentally damaging.Refining aluminum from ore takes prodigious amounts of electricity. Aluminum is readily recyclable. Toxicity/ Leaching: rate of leaching decreases rapidly as surface skins over reaction products. However, acidic water can aggressively dissolve aluminum. Healthy people typically have low levels of aluminum because digestive tract, skin, lungs are effective barriers to absorption, kidneys efficiently eliminate absorbed aluminum. Although some studies have suggested tentative link between aluminium Alzheimer's disease dementia, evidence as whole does not support causal association.23 Taste: May add slight metallic taste. Rock Mortar It is tough to surpass well-crafted rock tank beauty durability. However, popularity of rock tanks as choice new construction of water storage is fading to zero in industrialized countries. This is consequence of large amount of skilled labor needed to build tank, staggering amount of material to build even small tank, their tendency to leak. They remain attractive option labor is cheap, rock more accessible than bought tanks, bit of leakage to nourish their attractive patina of moss plants no great loss. specify rock mortar diversions in natural watercourses. It just feels right, is less intrusive than concrete rebar. One real factor is that floodwaters smash diversion, it's just more boulders sand in creek bed, not evil tangle of broken concrete dangerously protruding, twisted rebar. Dry-laid rock can be used sunscreen visual upgrade on tanks of other materials. (See Masonry in over Plastic, p. 47, photo at right.) Toxicity/ Leaching/ Taste: Same as ferrocement (they are plastered inside, so water contact surface is same). Concrete Concrete is especially popular large, municipal tanks. Most concrete tanks are made reusable forms, enable considerable effort expense of making suitable forms to be amortized over many tanks. Concrete tanks offer durability approaching that of rock, but much less material leaks. Pre-cast or cast-in-place concrete is good high strength is needed to meet external loads, in buried tanks, example. Toxicity/ Leaching/ Taste: Same as ferrocement. Brick This is another old-fashioned technique, good small, square tanks in non-industrialized nations. It is much easier quicker to work than rock. think this technique is under-utilized in modern construction in US, it is suitable small-sized tanks specialized shapes, valve boxes, clean-outs, etc.. Mexican masons on U.S. job sites know how to do these things, if only they were asked÷ Toxicity/ Leaching/ Taste: Same as ferrocement (they are plastered inside, so water contact surface is same). Clay Clay is rarely used bulk water storage outside of non-industrialized nations. It is heavy, brittle-- beautiful. (See photo, back cover. Minerals from evaporated water are source of patina on this old tinaja.) Clay is excellent material storing drinking water. Ceramic urns of 55 gal (200 L) capacity remain common in Burma. Toxicity/ Leaching: Generally of low concern. Glazes may contain heavy metals. Of particular concern is lead glaze on low-fired pots from Mexico. Taste: Unglazed, low-fired pots can add earth taste to water, but they keep it cool due to slow evaporation. Wood Wood tanks were common means of storing water in past. They are beautiful ingenious. wood expands wet, steel hoops contain expansion so plank joints seal tight against each other. Wood tanks are most commonly made of redwood, cedar, or oak. Oak tanks are used mostly wine. Wood tanks have lost popularity due to shortage of old-growth trees to make big, thick, close-vertical-grained heartwood planks--plus high cost, necessity of keeping tanks generally full to avoid drying out, tendency to leak slightly. number of new wooden tanks outside wine hot tub industries has dropped nearly to zero. main limitation of wood water tanks is that if you let water level drop, boards will dry out. If you raise water level back up slowly enough, walls will swell again seal, hardly any water will leak out. But if you let floor dry out, you may lose tank. Your best chance in that case is to tighten lower hoops, then put sprinkler or mister inside tank. If you're lucky, boards will swell enough after several hours that it will start to hold water again. In areas old wooden tanks were common, you may be able to buy them fraction of value of wood in them. got 900 gal (3.4 m3) redwood tank fifty bucks. put new hoops on it, sealed cracks special goop this application.24 floor eventually buckled it had nearly rotted through. However, it still holds water. slow drip goes onto orange tree, is happy to have it. (Photo, inside back cover.) There's no way to get drain sump in wood tank, but you can put in floor drain, install tank tilted so floor slopes towards it. To install floor drain, drill hole drain pipe, then mill round depression around it router, then install bulkhead fitting in it. Attach to outlet using rubber coupling hose clamps. This will enable you to unhook drain to move tank, will reduce chance that plumbing will crack as tank shifts around. Toxicity/ Leaching: No issues, except oils that make cedar so rot-resistant are toxic to humans as well as to microbes; cedar tank is not suitable potable water storage. Caution: Some folks make water tanks out of treated marine plywood. think both shape (big, flat, weak surfaces) toxic, non-durable material are ill advised water tanks. Taste: May give water slight, non-objectionable wood taste. Plastic Plastic tanks are low cost, lightweight, impervious. They are good choice small- medium-sized tanks residences farms. downside is that they are not available in big sizes, they turn into difficult-to-recycle trash relatively rapidly, bought tanks generally have problematic combined outlet/drain. All of these drawbacks except small-size limitation can be overcome by techniques described in Masonry in over Plastic, p. 47, at cost of sacrificing possibility of relocating tank. plastics are best? danger of leaching from plastics depends on many variables. It is both poorly understood controversial. American Plastics Council, example, has different take than Greenpeace. Greenpeace is calling worldwide ban on PVC, move gaining traction in number of countries. figure from Greenpeace (at right), modeled on food pyramid, proposes proportion of plastic use based on ecological impact. Toxicity/ Leaching/ Taste: bottom line water tanks is to use HDPE, use as little PVC as possible. (See Table 7 overall ratings by specific plastic, Appendix C less common plastics, Water Storage Extras6 exhaustive survey of what is known on this topic.) High Density Polyethylene (HDPE #2) HDPE is preferred plastic water tanks, it is most commonly used material. It is relatively innocuous in its manufacturing, use, disposal, at least compared to other plastics. tank is no longer serviceable, plastic can be reused. Polyethylene is not currently recycled--it is cascaded to uses less stringent materials requirements. High-density polyethylene is also preferred plastic plumbing. It can should be directly substituted PVC in most piping applications. However, use of polyethylene tank plumbing details is alien practice in U.S. One example of how such connection can be accomplished is shown in Figure 18: Drain Options, p 61. You can always insert threaded adapter barb in threaded in- or outlet go polyethylene from there. To reduce leakage in HDPE pipe, cover barbed connectors silicone before clamping, or weld lines.16 Toxicity/ Leaching: Low toxicity. Taste: Unfortunately, polyethylene can impart plastic taste to water, though this is rarely noticeable in large tanks. Keeping tank shaded will reduce this effect. Ethylene Propylene Diene Monomer (EPDM) EPDM is best artificial pond liner. It is synthetic rubber resistant to heat, ozone, UV light. It is able to stretch quite bit without tearing. (There are photos of EPDM liners under Ponds, p. 20.) There is little data on leaching of EPDM, although it is generally considered to be pretty inert. It is more environmentally friendly building material than PVC. EPDM is manufactured both roofing ponds. There is controversy about using EPDM roofing ponds, some claiming it can be used if washed. Actually, both EPDM roofing pond materials need washing, as they are dusted talcum powder to keep plastic from sticking to itself. If storing potable water, make sure that product meets NSF Standard 61 contact potable water. In theory EPDM can be recycled, but it's not as easy as dropping it off at recycling center. It is thermoset material cannot be re-melted. It can be ground up used something else. However, you may be hard-pressed to find recycler to take old pond liner off your hands. Toxicity/ Leaching: Low. EPDM sold as roofing material may have toxic coating. Taste: Little or no effect on taste. Fiberglass (Glass Fiber-Reinforced Polyester, GRP) Fiberglass tanks are very strong, lightweight, non-corrosive. Fiberglass is quite bit stronger more expensive than HDPE generally considered to be higher quality. It is certainly superior to HDPE underground tanks due to its high strength. Exceptionally nasty solvents are used in resin used to make fiberglass. Toxicity/ Leaching: There are reports of high concentrations of solvents in newly constructed fiberglass vessels (flushing is recommended). literature is strangely quiet on long-term health effects of drinking water from fully cured fiberglass tanks.6 Taste: There appears to be little effect on taste after full curing. Epoxy-Coated Steel or Concrete This is like liner bonded to tank. Epoxy-coated steel is good choice large, durable tank. This is popular option big municipal-sized tanks. See Polyamide Epoxy in Appendix C look at health ecological effects. Toxicity/ Leaching: Moderate leaching concern. Make sure coating meets NSF 6120 standard potable water. Also make sure that epoxy is fully cured before filling tank, flush first few tankfuls of water. Taste: There appears to be little effect on taste after full curing. Masonry in over Plastic You can turn cheapo plastic (essentially disposable) tank into first-class, high-performance, lifetime tank by combining it masonry. This overcomes many of shortcomings of both materials. In conventional combination (metal/ plastic liner), metal can corrode light membrane puncture or tear. If you combine plastic tank ferrocement or stone masonry, there's nothing to corrode, thick plastic tank won't puncture or tear. full retrofit consists of: making sloped masonry floor drain sump dedicated drain adding clean outlet adding masonry around outside (See photo at right, Plastic Tank Drain Retrofit, p. 60) Masonry outside provides complete shade sunscreen, extending life of tank to approximately forever. masonry can be dry-laid rock or stucco over chicken wire. bigger tank, harder retrofit gets. masonry floor retrofit provides better drainage cleaner outlet water. masonry should be added tank full of warm water, .e., at its maximum expansion, so plastic not masonry take tension load. Toxicity/ Leaching/ Taste: Same as plastic tank. Galvanized Steel Plastic Membrane addition of interior plastic membrane enables much lighter-weight galvanized tank to have acceptable life span. trade-off is enjoying low cost versus losing flexibility to add inlets outlets, reducing repairability maintainability, increasing difficulty of getting good drain. This composite tank design uses very lightweight steel strength, membrane waterproofing. It seems like very efficient use of resources. However, have hard time getting myself to truly embrace something made out of plastic thinnest possible metal. It essentially amounts to repairing tank in advance, knowing it is too thin to hold water long. brilliance of it is that without water on metal it will last longer, installing membrane from get-go is cheaper than retrofitting it later tank is old, wet rusty. This is relatively new tank technology. Time will tell how well these systems hold up. Toxicity/ Leaching/ Taste: Leaching hazard taste depend on membrane material, can be PVC (bad), epoxy (supposedly OK after curing), or polyurethane (bad in production, not clear how it is in use6). Interior Membranes Repair If structurally sound tank of any material starts to leak, you may be able to get some more life out of it by adding plastic membrane inside. Toxicity/ Leaching/ Taste: Depends on material, same as Galvanized Steel Tank Membrane, above). Plastic Bladders This is class of storage water is contained within non-structural plastic membrane, is supported by some other structure. There are many options here, ranging from water bed bladder, to system giant slug of membrane is cocooned in underground culverts.25 'm not particularly drawn to this approach. One objection is that plasticizers in flexible membranes tend to be more toxic than same plastic in rigid form. (Don't drink from your water bed--see Materials/ Situations to Avoid, p. 39.) Beyond that, it just seems sketchy to store boatload of precious water in what amounts to plastic bag. would think it would pinhole all over, or possibly tear unless you were fanatically careful about installation service. However, in practice, these systems seem to be working so far, they do offer tremendous cost savings. Toxicity/ Leaching/ Taste: Depends on material, same as Galvanized Steel Tank Membrane, p. 47. Goat Bladders, Leather, etc. Animal skins have long been used to transport water. Leather vessels keep water cool by sweating through walls. Well into dispiriting research on toxic leaching, found account from another researcher who was so appalled by threats that he was ready to go back to storing water in goat bladders, like his ancestors. have to admit that after reading countless abstracts of studies about nasty chemicals from plastics, contaminated cements, etc. idea does have certain appeal. Toxicity/ Leaching: In case of leather, tanning chemicals may enter water. Taste: Most skins impart taste. Tank Footings Floors firm, well-drained footing is essential long tank life, especially large tanks. These footing considerations apply to all tanks: earth under tank should be well-compacted free of large or sharp rocks. surface drainage should be away from tank in all directions (except some runoff harvesting tanks). Tanks on benches cut into slope should be resting entirely on undisturbed soil (cut), not on tailings from excavation (fill). Steel tanks are usually set on bed of gravel. This slows corrosion of bottom of tank by keeping it dry underneath. compacted soil under gravel is ideally sloped to one side (or all sides--see figure at right) so moisture is less likely to get under tank, softening soil condensing on tank bottom. Coarse gravel is preferred, to promote drying air circulation under tank. Plastic or fiberglass tanks can be set directly on firm, rock-free soil. If there are rocks, or surface is uneven, floor of tank can be protected thin layer of compacted sand or pea gravel that won't wash away. (Plastic isn't strong enough to bridge large gaps between coarse gravel.) tanks bear on footing over 800 lbs/ft2 (3900 kg/m3), concrete footing steel support stands is suggested to prevent movement in wind or earthquakes. floors of ferrocement or concrete tanks can be poured directly onto firm soil free of large rocks. If natural surface is too uneven, it can be smoothed addition of layer of sand. walls of concrete tank should be buried at least to level of floor inside tank. This is to reduce chance that erosion will undercut floor, possibly leading it to crack. Large roots under tank could heave underneath it, possibly cracking floor. If roots can't be removed, they can be covered over raised layer of gravel; roots won't grow into gravel if it doesn't have water in it. If soil under tank is disturbed, re-compact it well. If only available site has huge rocks or bedrock under it, try to build entirely on rock, otherwise difference between how soil rock compress could crack tank. community in Mexico built 100,000 gal (380 m3) cistern by sealing space between vertical walls of exposed bedrock rock wall pouring footing on earth between. This cistern has always leaked. suspect that problem is that earth under tank moves slightly as four hundred tons of water press down on it then are removed. If your footing is perfectly smooth stable, load on tank floor will be insignificant. If it is not, resulting strain can crack floor walls. ( explanation of radically different ways flexible stiff tank floors of different shapes behave structurally, see pages 91 112.) Plastic, fiberglass, ferrocement, or concrete tanks can be partially buried. tank should be capable of withstanding press of wet soil from outside in without collapsing, should be leak-free so water moving through soil does not contaminate it. would hesitate to bury mortared rock tank. There is strong likelihood that roots will find some crevice in masonry, work their way through it to water inside, possibly damage tank as roots grow in thickness. Tank Roofs Roofs can be structurally integrated walls, or separate structure set on top. In case of separate structure, good attention must be paid to details of critter-proofing excluding roof runoff at roof-to-wall interface. In case of structurally-integrated roof, it can be advantageous to make roof-to-wall joint continuous pressure-tight, so space under roof can fill water. This enables tank to store significantly more water. integrated, pressure-tight roof will typically be of Ïunibody" material such as plastic or ferrocement, in conical or dome shape. tanks more than fifteen feet or so in diameter, central pillar of steel-reinforced concrete or steel pipe can be added to help support roof. This can be convenient place to add integral ladder. Domed roofs are most structurally efficient. However, if you intend to make roof of concrete, wood or steel, flat roof will be much easier to build or support straight materials like wooden beams. Conical, hexagonal, or octagonal roofs are compromises that offer advantages of both flat domed roofs. (See Appendix B more information on structural properties of different shapes.) Roofs made wooden trusses conventional roofing (like house roof) can be cheaper easier to make big tanks. They have disadvantage that they are all but impossible to seal against spiders whatnot. Note galvanized sheet steel roofs on square or rectangular tanks: It is easier to slightly adjust dimensions of tank so sheets neatly cover it (e.g., Ï5 sheets wide by 1.5 sheets long"). This helps to minimize amount of cutting, is relatively difficult task. multi-sided tanks this is more difficult, but should still be kept in mind.16 Water-Harvesting Roof If your tank is harvested rainwater, why not harvest rainwater from roof of cistern, as well? This is easiest cement tank into rainwater harvesting Ïwings" can easily be incorporated--see large photo on front cover, top left photo on page 57. latter has two foot (60 cm) Ïwings" increase catchment from its own roof about 40%. 60" (1.5 m) of rainfall year, this 13,000 gal (50 m3) tank will catch enough rainfall in average year to almost fill it once-- significant contribution. cistern roof is domed. wings spring back up from low point at rim of dome. resulting channel slopes to low point, there is both drain inlet into cistern, movable plugs. There is photo of this cistern from below in section Rock Mortar, p. 43. bottom photo on p. 43 shows cistern fills entirely from water harvested from its own roof--in near desert at that. There is more on water harvesting roofs in our book Rainwater Harvesting Runoff Management.3 Tank Costs Figure 14 (left) summarizes typical costs different size tanks: all materials, cost per gallon drops steeply at first, then less dramatically as tank size increases. Really Cheap Storage If economy is overriding consideration, here are some suggestions really cheap storage: Salvage 30 or 55 gallon drums can often be scrounged little or nothing. bungs often have 3/4" pipe threads, facilitating attachment of inexpensive plumbing, example small diameter polyethylene tubing. Drums can also be drilled, tapped, threaded, or fitted bulkhead fittings to make inlets outlets in any position. Tote bins used palletized, bulk transport of liquids. They can be made into passable small tanks, if they've contained something non-hazardous. They are usually 275 gal (1 m3) HDPE containers. Above-ground swimming pools are cheapest, funkiest storage going. Not long-term solution, but you can't beat cost. plastic walls are usually PVC. Ponds can be relatively inexpensive large volumes of water. Aquifers usually don't cost anything can store vast amounts of water. Regulatory Requirements Many, if not most, water tanks are installed little or no regulator involvement, but rules enforcement can vary quite bit depending on you are. You'll need to inquire locally to find out what you'll be subject to. Water storage may be subject to zoning, building department, fire department, health department rules. If you have homeowners' association, it may regulate water tanks, perhaps just because they are structure. Your insurance company may have rules or incentives relating to water storage as fire safety resource, flooding hazard, or simply as another asset to insure. Some of rules you may encounter will be consistent your own interests, some will run counter to them. You may run into rules concerning: Zoning You may or may not be allowed to be build water tank within building setbacks from your property lines-- zoning department can tell you. Architectural Guidelines In some neighborhoods, rules may prohibit above ground tanks. beautiful ferrocement tank attractive shape color, or one that looks just like boulder, may be able to overcome anti-tank prejudice. Building Department It will generally be building department that enforces plumbing code requirements about pipe sizes, materials, placement, etc. Tanks over certain size may require permit--5000 gal/ 18.9 m3 in our county. Large, constructed tanks may require permit engineer's stamp on structural plans. Some of tank-specific requirements we've heard of: Lockable lid to guard against malicious contamination drowning hazard Sealing lid to guard against entry of roof runoff creatures Overflow mosquito trap Soil report structural soundness of soil that supports tank Fire Department fire department may require that hydrant be attached to tank, certain-sized connection (4" in our area). They may require Ïset-aside" or reserve of specific size (2000 gal/ 9.5 m3 in our area) that can only be accessed via their hydrant--not bad idea, if you want them to be able to save your house. This can be accomplished by putting hydrant outlet at bottom domestic supply outlet higher up. Health Department health department may have their own rules, or defer to building department. vector control department may want to ensure that your water storage does not breed mosquitoes. Hazards of Stored Water How to Avoid Them It is easy to get so engrossed in operation of system as intended that it doesn't occur to anyone that water tank also works as, instance, child trap. Fulfilling legal requirements (above) may help reduce some hazards, but you should also take direct look at hazard reduction. (Note: This section covers ways that stored water can harm things. Ways that things can harm stored water are covered under Protecting Stored Water, p. 77.) Drowning Drowning can be real hazard stored water, primarily children. two strategies to reduce drowning hazard are: Limit access to water, e.g., fence, locked access hatch, or removable outside ladder. Provide easy way out of water, e.g., built-in ladder on inside of tank, or steps on sides of reservoir. water tank access hatch in middle no built-in ladder is especially hazardous. Even resourceful adult might drown before they could figure way out of tank. At least leave knotted rope dangling down. Structural Collapse What will happen if water tank topples? Could water tower fall over squash house? Maybe it should be bit further away. Could earthquake or landslide tip tank off of its pad on steep hillside, result that it steamrolls over houses below? engineering of water tanks is not intuitively obvious. structural loading per unit of area is usually lower than people think, total loading higher than people think. (See also Appendix B, Structures, p. 91, Protecting Stored Water, p. 77.) Flooding What will happen to water if tank or pipes break? If answer is Ïnot much," then you don't need to dwell on it. If life-threatening situation might result (like one described on page 91), safety may be main design factor. Pestilence Biological hazards in stored water should be minimal or nonexistent good storage design if water was clean in first place. (See How Water Quality Changes in Storage, p. 9.) Toxic Contamination Assuming there are no toxins in incoming water, route toxins to get into stored water is by leaching from storage vessel or plumbing. Toxins from outside can also permeate through walls of plastic containers. Leaching is discussed in general in How Water Quality Changes in Storage. Leaching hazards from various materials are discussed in Table 7: Materials, p. 40, in more depth in our Appendix C. Permeation is discussed on page 78. There is bunch more info on this issue in Water Storage Extras.6 Liability Exposure If your water system incorporates hazard that you should have been aware of, or if your water storage doesn't meet legal standards, you could be sued if someone or something comes to harm as result. Good design will minimize chance of this happening, or your being liable if it does. Water Tanks Special Applications Pressure Tanks Pressure tanks are alternative to elevated tank to provide pressure. They typically have pressure switch that controls pump that pressurizes them, air bladder that stores enough pressure to push out third or so of volume of tank before pump has to switch back on, air valve to adjust air pressure. Pressure tanks are usually small--30-50 gal (75-190 L). Their advantage is that they are far less expensive than elevated tank piping to it. Their disadvantage is that they provide little water security because power goes out, there is almost zero reserve. If you can, situate main tank higher than water use points, so that water will still flow, without power, albeit at low pressure. As last resort, you can put in really big, expensive pressure tank to get more reserve (see photo, p. 30). Break Pressure Tanks These aren't storage, though they do have Ïtank" in name. Break pressure tanks provide air gap that releases contained pressure in pipe. They then funnel water into another run of pipe. Strategically placed, these tanks can reduce amount of expensive, pressure-resistant pipe in system. break pressure tank has inlet line, provision venting access, outlet. They are usually small, accommodating just moment's flow. Hot Water Storage Some of same techniques described under Freeze Protection (p. 73) can be used to make tank that holds warm or hot water. Hot water tanks some solar water heaters use Ïthermos" effect to great advantage-- high vacuum between walls of glass pressure vessel prevents heat loss by convection or conduction, silver coating reflects radiant heat loss. Hot spring water is often highly corrosive, especially resistant materials may be required plumbing. One hot spring found CPVC to be most resistant material; another, only copper pipe high-temperature silver solder would hold up. Tanks Transporting Water transport, ideal water container would be strong lightweight, would resist sunlight, would neither leach nor slough off nasty stuff into water. In stationary tank, great sheets of rust that peel off just harmlessly settle to bottom, but in mobile tank, water sloshes stirs everything up. Stainless steel is ideal, followed by polyethylene. Chapter 4: Common Features of Water Tanks This section covers features common to almost all water tanks. There is more information on optional features in Chapter 5. (Inlets in general are covered here, while you'll find inlet float valves there.) Inlet inlet is water flows into your tank. preferred practice is each water source to have separate inlet. type of water source determines on tank your inlet needs to be located. If water source is well, or otherwise below tank, inlet must have air gap to surface of water, must be pipe diameter above highest level water can reach overflow is flowing at full capacity. This is to avoid siphoning tank water in reverse through inlet line, possibly contaminating well (see Figure 19, p. 62). inlet should be as high in tank as possible so that overflow can be high. spill point (lowest point) of overflow in turn determines maximum useful storage capacity of tank. high inlet/ overflow will help get your money's worth out of tank capacity. If water source is gravity-flow water, inlet can be just about anywhere. tank water can't flow back uphill to contaminate source. inlet at top is convenient installation of inlet float valve to automatically shut off incoming water tank is full (see p. 66). inlet near bottom ( diffuser) can facilitate settling (see p. 68). Caution: If both well gravity flow supply tank, overflow must be high enough capacity to prevent gravity flow water at peak flow from raising tank level to it drains into well. check valve at bottom of line in well provides some protection against backflow, but since these commonly leak it is not good design practice to rely on them this function. There should be shut-off valves, unions, bypasses, or some other way to shut off or divert water supply to all inlets so you can service tank. Outlet outlet is pipe through you get water out of your tank. It should be as close to bottom of tank as possible without being so low that it sucks settled muck off bottom. This arrangement will maximize useful storage capacity, helping you get your money's worth out of tank. You can create emergency reserve (e.g., fire) by installing low outlet reserve, mid-level outlet ordinary use. There should be shut-off valve on outlet, to stop flow of water in case of massive leak, so you can work on system. Storage in non-industrialized countries often doesn't have outlet (or drain). This simplifies construction all but eliminates chance of catastrophic water loss. water is taken out hand-held container, bucket on rope or pump. Service Access There must be provision getting inside tank inspection cleaning. In case of tank that is so small that your arm can reach from top to bottom, it is sufficient to have arm-sized opening. Otherwise, you need opening of about two feet (60 cm). tall tanks, it is convenience safety measure to have built-in ladder, at least on inside. Rungs or stepping-stones should be spaced one foot apart vertically (30 cm). integral inside ladder eliminates possibility of introducing contamination along portable ladder. It is also convenient to have pressure-tight service access door at ground level, can be opened construction major service, to save effort of climbing up outside down inside. If tank (or diversion) receives uncontrolled surface runoff, manhole at bottom can be godsend cleaning out truckloads of accumulated soil, rocks, vegetation. Drain drain is how you get sludge, last of water, wash water from cleaning out of your tank. practical consequences of well-drained tank are: tank that is cleaned much more frequently perfectly by happier cleaners, leading to: cleaner water at tap, especially tank levels are low amount of muck entering tank is high drain is most neglected area of conventional tank design. We're going to provide many pages of information here to fill void. What will happen if you ignore drain issue? If your water is sediment-free, not much. If your water contains sediment, however, you'll be happy you took trouble to learn about drains. Tanks No Drain classic tank design leaves drain out entirely, so outlet doubles as drain. This brings such negative consequences as: level of settled sludge reaches level of outlet, it will suck sludge out into pipes. water level is low, water falling from inlet will stir up sludge, occasionally yielding concentrated sludge brew at taps. Draining tank completely cleaning is extremely tedious process using buckets, shovels, finally sponges. There isn't easy way to get water from washing inside of tank out. Bottom line: tank doesn't get cleaned often or well. What do tank manufacturers think? That their clients have totally crud-free water? Don't mind sucking sludge into their pipes? Have nothing better to do than remove vast puddle of mucky water one sponge full at time? 50,000 gal (190 m3), bolted, galvanized steel tank at right had no drain. lowest outlet left more than ankle-deep sludge water on bottom--several truckloads. It was all-day affair several muck-covered volunteers toting brooms, buckets, shovels, sponges to get it halfway clean. Each successive rinse was agonizing effort, was indiscernibly cleaner than last. Time energy invariably ran out before sludge did. We partially remedied this sorry state by welding 4" drain flush under floor (photos figure at right). This solved problem of getting most of sludge water out. However, absence of slope to floor still left last little bit exercise in frustration. You'd sweep puddle towards drain, while drain would intercept narrow swath of current, rest of water would just swoosh past curve around tank to other side. If these drainage problems had been anticipated in original installation, we could have welded drain right at edge (before rubber gasket was in place--see photo above), then installed tank ever so slightly tilted, drain at low spot. tilt of 1/2% or 1% would be hardly noticeable, but would give tank-cleaners huge edge; they could feed rinse water from inlet (at high side, of course) sweep increasingly clean water towards drain at low point. This bit of tilt also could squeeze in another inch or so ( few hundred bucks' worth) of water level, by making more room to install overflow at high point. Drain Location Orientation Some tanks come horizontal drainpipe at floor level. capacity of such drain is very low tank is empty. big drain thin puddle of water on floor has only tiny part of its cross-section wet, so it can drain only trickle of water. What this means is, you go to clean tank, wide, puddle will deepen until enough of cross- section of drain is wetted that it can accommodate rinse flow. Without sump, drain flows slower slower lower water level gets, rinsing is still exasperating operation. Drain Sump sump-- depression around drain--increases drains' low-water flow capacity tremendously, provides place sludge to Ïcatch" cleaning wide, gently sloped floor. design water tank to be built from scratch, make distinctly sloped floor (1-2% or more), sump drain at lowest point. 've heard from other tank makers that flat floor sump works very well drainage, this is clearly easier to make (Figure 18, at right). To clean tank sloped floor, sump, drain, you just open drain turn inlet on. Inside tank, fill buckets from inlet splash water on roof, walls sloped floor, then sweep them off, then rinse more water. In hour one person can clean large tank almost perfectly, from start to finish. Plastic Tank Drain Retrofit In Masonry in over Plastic (p. 47) we described many benefits of combining masonry plastic. You can achieve easy cleaning cleaner outlet water from plastic tank by fixing combined outlet/ drain problem. Simply put tank you want it life, then pour sloped concrete floor inside, as per picture at left drawing below. Drain Components drain should always be bigger than you think. ankle-deep water pressurizing pipe flow rate is very low. Two pipe sizes bigger than inlet is about right. That is, 4" drain tank 2" supply, 2" 1" supply. drain line can be capped instead of valved, since it isn't used often, usually drain won't have water gushing out any more it is time to put cap back on. cap is better than plug because it goes onto male outlet threads won't catch crud, whereas plug fits into female threads that are apt to fill sand. ball valve will allow ease of opening closing; removable cap will save you money. If your context is rustic you really need to save money, flower stalks of yucca cacti make awesome plugs--giant corks that can take several feet of pressure (Figure 18, preceding page, bottom left). Overflow Like overflow in your bathtub, overflow in tank establishes maximum water level, carries away excess water. overflow should be located as high as possible while leaving room air gap between maximum water level ( level water rises to it is overflowing actively) inlet of any well connected to tank (see Inlet, p. 55). overflow should be big enough to accommodate full flow from all inlets. Usually this means it needs to be bigger than inlets. just little pressure to push water through, 4" overflow might be needed to accommodate all water gushing from 2" high-pressure inlet. sizing of overflow depends lot on what happens if its capacity is exceeded. If water will just flow harmlessly out tank's vents or access hatch, that's no big deal. But if overflow is only way to relieve pressure you don't have one or it clogs, you could end up pressurizing your whole tank as in Figure 32: Water Pressure Depends on Depth Alone, (p. 91), result that tank blows up. overflow is great opportunity to be rid of stuff floating on surface of water. Why dump clean water you can be rid of dirty water instead? To make most of this opportunity, orient overflow opening in same plane as water surface (see Figure 19, below). floating stuff rides on top layer of water molecules, layer that holds together like tablecloth as it is pulled out overflow. large-diameter, horizontal overflow, less water comes from deeper in column, so you're dumping dirtier surface water. Also, this overflow geometry surface sheet gets tugged on more, pulling floating crud out of furthest reaches of tank. If overflow opening is at right angle to water surface, substantial fraction of flow is drawn from lower in water column, you'll mostly be dumping clean water. If you install overflow its opening entirely under surface, it will draw only from mid-water column, leaving surface covered dust, leaves, mosquito larvae. If you use large, horizontal overflow, you can place it slightly higher in tank. extra two inches of water depth in tank twenty feet in diameter equates to 400 gallons more storage.m This is worth at least $600, quite bit more than cost of extra effort materials. overflow should not have shut-off valve on it. Exceptions Now that you know all about overflows...you may not even need one. If water source is above tank, that itself protects it from contamination-- air gap below inlet is not needed. If water source is not expected to overflow extensively ( example, if you have float valve or pump switch normally shuts off water supply tank is full, or if supply is at pressure corresponds exactly to maximum water height in tank), access port or air vent can double as overflow, or access port can Ïtriple" as access, air vent, overflow. Critter-Proofing ALL points of ingress to system should be critter-proofed. Not only mosquitoes love water. Thirsty rats are particularly ingenious about getting into water tanks dying there. There's nothing like pulling pieces of dead rat out of your water lines to get religious about details of critter-proofing. Block entrance points using mosquito net, welded wire mesh, closed valves, check valves, water seals, or forceful outward flow of water. Water seals (like traps on drain lines) will stop flying insects from getting in, but they won't stop rats. overflow critter-proofed mesh can clog, causing pressure to build in tank, possibly exploding it. If you have overflow that is too critical to restrict wire mesh, swing-check valve is answer (see Figure 20 on preceding page). Air Vent If air can't get out of tank, water can't get in. There needs to be way air to get in out of tank, one is screened against insects rodents getting in, doesn't admit much light (see Sunscreen below). vent geometry should preclude runoff from tank roof from entering. You should generally only have as much venting as is needed to make way incoming water, isn't much at all. If you have huge airflow, you may lose significant amount of water to evaporation. Sunscreen Shade Sun plus water equals base of food chain. Almost all water sources have enough trace concentrations of nutrients that if you put them in sun long enough, some algae will grow. Then something will want to eat algae, so on÷ Metal masonry tanks completely block sunlight. Plastic tanks should be black /or indoors, buried, or covered, to prevent light from getting in water. (See Masonry in over Plastic, p. 47.) There is every advantage to keeping water cooler in summer. You can put tank in shade paint outside of it white, silver, or unobtrusive, light version of local rock or vegetation color scheme. This will lower water temperatures thermal expansion/ contraction stresses in above water portions of tank. (Note: black plastic tank painted white will be both cool, dark inside. unpigmented, cloudy white plastic tank will quickly degrade algae will grow vigorously inside.)Chapter 5: Optional Water Tank Features In this chapter we go over various optional gadgets can enhance function of your system. Be aware, too, that there are host of other possible options we're not going to get into (remote flow meters, automated injectors treatment chemicals, online monitoring meters turbidity, chlorine level, etc.). Inlet Meter, Filter, Gauges If you want to optimize use of resource, measure it. Our water system has two wells spring, each meter on inlet, just before water tank. Each house that is connected to water system has meter. regular readings, these meters provide information valuable management of system, such as amount of water capable of being produced by our wells spring in wet dry seasons, consumption in wet dry seasons, etc. My next house is going to have water meter set into tile above kitchen sink to keep us continuously appraised of our water consumption. in-line filter protects meter or float valve on inlet. Place it just before meter or valve, to keep their mechanisms from clogging chunks of rust from supply line. Place in-line inlet filter just below Ïbreakaway" section of line from creek direct system--that is, just below point line is threatened floodwaters. If filter in creek gets knocked off, this in-line filter will keep whole line from filling gravel. Pressure gauges can tell you level of water in tank remotely, operating or static pressures in supply lines, etc. Inlet Float Valve float valve on inlet is useful shutting off flow from gravity flow water supply tank is full. This not only avoids pointless removal of water from nature, it will improve quality of water in your system. One water system worked on didn't have float valve years. Every rainfall, springs would flood inlet would gush muddy water full blast into tank day night. Most of muck would settle in tank, while clean water poured out overflow. Inlet Combined Outlet Under some circumstances it is desirable to combine inlet outlet functions in same line, through water flows both into out of tank. This is most advantageous long lines. Instead of having two lines, you have just one, splits at tank into inlet outlet forks (see Figure 21). example of this application would be gravity pressure tank-- tank that water is pumped up to, from it runs back down into system. This is frequently function of water towers they are often plumbed this way. If gravity tank is connected directly to well (as in Figure 21), there is some trade-off in water security. If well pump check valve leaks, tank can drain back through leaking valve into well. If water in tank happens to become contaminated while check valve is leaking, well can get contaminated also. Discharging well into storage tank at wellhead level, pumping to higher storage tank from there can circumvent this issue, can be legal as well as practical. Inlet Aerator Aeration is process of breaking water into fine droplets mixed air. This creates large surface area-to-volume ratio. Oxygen can readily dissolve into water, gasses dissolved in water can readily escape. Certain kinds of water quality problems can be improved by aeration; example, manganese iron oxidize to less objectionable form.28 Noxious gasses in water, such as hydrogen sulfide chlorine can also be driven off more rapidly by aeration. If there is enough pressure, inlet can be aerated by capping it sprinkler or mister that thoroughly mixes water air in top headspace of tank. If there is little pressure, water from inlet can be broken into droplets by passage over tower of tiered screens or slats. aeration to be optimally effective, there needs to be enough ventilation to move oxygen in undesirable gasses out of tank. Inlet Diffuser to Improve Settling Turbidity (suspended solids) generally settles out storage in tanks. One community worked was faced tightening regulatory noose was requiring them to meet very stringent turbidity standard water from their springs. (Less than one NTU, equates to about 10 foot visibility). We replumbed their two 50,000 gal (190 m3) storage tanks to reduce spring water's turbidity as much as possible. (See Figure 22, Inlet diffuser, next page.) Instead of letting water level fluctuate in both tanks, dedicated one as spring water settling treatment tank. Before, spring water was introduced at top, hope that turbidity would settle out before reaching outlet (also at top). Instead, we ran new line from inlet float valve down to ring of pipe knee height from bottom, finger-size holes drilled in it every few feet. water ( suspended solids) exit in diffuse ring around entire bottom of tank, then flow ever so slowly up entire water column of tank. Arranged thusly, suspended solids start almost at bottom, we want them to settle, would have to float up nearly twenty feet against force of gravity to get to outlet, something they are unlikely to do. outlet of settling treatment tank is almost at same level as overflow, so tank is always full. Thus, there is never low-level situation inlet water is plunging through air to violently stir muck on bottom. In terms of storage, system now provides emergency reserve can be accessed by opening valve, is secure against accidental loss from catastrophic leak or unnoticed supply interruption. Outlet Screen or Filter If there is reason to believe that something might come out of tank could clog lines or valves downstream, it is cheap insurance to have screen over outlet. clog will be easier to deal there than elsewhere in system. If getting into tank to service it is too much hassle, you can use in-line filter just outside tank. Variable Height Outlet If your water supply is so tight that accidentally draining your tank would be disaster, consider installing variable height outlet. This is flexible or hinged extension to outlet on inside of tank, can be manually raised or lowered to track just below water level in tank, so there isn't much water above outlet. If there is leak or some other problem, only water that is vulnerable to loss is volume between surface level of outlet. (See Figure 22, Variable Height Outlet.) Outlet Float water in tank is generally cleanest about 6" (15 cm) from top of water. You can take water from this level by extending outlet on inside of tank flexible line float. Water Hammer Air Cushion If you have long water line high rate of flow someone slams ball valve shut at tank inlet, moving water column is like battering ram impacting closed door. resulting pressure spike can be many multiples of static pressure can easily blow pipe up. To avoid this scenario, you can: use gate valves, are not possible to shut suddenly use high-pressure pipe put big warning signs on valves in several languages install air cushions air cushion is simply part of plumbing that traps enough air so that water hammer pressure spike hits it, it cushions blow. You can buy bladder-filled ones or make your own (see Figure 23, above). Put them in place in system they will be self-draining system is drained. Otherwise, they will eventually fill water, reducing their effectiveness. Level Indicators It is reassuring to know how much water is in your tank, convenient to be able to determine this without having to climb to top look in. There are several gadgets that can help you accomplish this: Float float in tank raises lowers weighted marker on outside of tank. These common devices are simple reliable, so long as weight float are heavy enough to keep rope or cable that connects them from sticking it passes through tank. (See Figure 24, Level Indicator, next page) marker can be positioned so that it can be seen from far away. Note that marker is at bottom of tank, water level is at top--this takes bit of getting used to. Air Pressure Level Gauge air pressure level gauge uses bulb to pump air into tube immersed in water. tube is all way full of air, pressure of column of water trying to push back into it can be read as water depth on air pressure gauge. line gauge full of air (instead of water,) there is nothing to freeze in cold climates. Clear Tube clear tube that covers same height span as tank can be used to directly read water level. tube can be marked reference lines. tube must be either filled chlorinated water, kept in shade, or drained not in use, or it will grow algae, become difficult to read. Remote Pressure Gauge ordinary water pressure gauge anywhere in system can show water level in supply storage tank, provided water use at moment isn't so high as to cause significant pressure drop in line. You can get pressure gauges that read in inches, or take ordinary pressure gauge add your own scale. gauge will do more accurate job of showing exact water level in tank if it has these features: big face (4" (10 cm) is good) range just encompasses maximum pressure in your system (if pressure full tank is 54 psi, 60 psi gauge will give better reading than 100 psi gauge) high precision (±1% or better) Electronic Level Indicator bought electronic level indicator can give remote reading anywhere you can run wires or radio signal. Calculate Gallons Per Inch All gadgets above will give you readouts of water depth. To translate this into water volume, you'll need to measure or calculate gallons per inch of water depth (or cm per m3). You can use our Water Tank Calculator6 to help calculate volume. If your tank is shape that is too strange to calculate, empty or fill it through water meter, make mark at water level that corresponds to each increment of volume. Knowing how much water use (or production) is represented by given change in water level will sharpen your monitoring of system. Ozonators Ozone is great alternative to chlorine disinfecting water. (See Hazardous Disinfection By-products, p. 10, reasons not to use chlorine.) way ozone treatment typically works is by generating ozone UV lamps or corona discharge equipment, then pumping it through diffuser or diffusers in tank or injecting ozone directly into tank feed line. water tanks are integral part of such treatment system. tank full of water saturated dissolved ozone can handle spikes in amount of incoming debris /or pathogens, whereas low, steady output of ozonator by itself could easily be overwhelmed. (See photo at right Figure 24, Ozonator.) Drain Extension or Baffle unglued extension from drain to level above sludge in bottom of tank will enable drain to be used as both drain outlet. extension pipe slipped in place, water leaves tank above muck level-- clean outlet. Pull extension out, muck will suck out of drain. In case of outlet on side of tank, baffle could deflect its suction upward, so it doesn't suck crud off bottom of tank. (See Figure 18: Drain Options) Outlet Overflow Curves Sharp angles transitions at outlet or overflow create turbulence that limits peak flow. If you form gently curved transitions that smoothly funnel accelerating water flow into narrower space, you can get higher peak flow. ideal shape is like graph of water speed; wider flow is just starting, narrowing as it speeds up, then constant as it's made it up to speed into pipe. There is photo of very successful curved overflow runoff diversion dam on p. 25 drawings of flared overflows on pages 62 64. Pump Controls, Alarms, Switches simplest pump control is to manually turn your pump on, you hear or see water pouring out overflow, shut it off. You can install float switch will turn on your well pump automatically water reaches specified level, turn it off again tank is full. switch can be hard-wired to well pump, or connected via radio transmitter. alternative pump control system uses special float valve pressure switch. special float valve shuts off inlet all at once tank is full. Pumping against closed valve, pressure on line will spike upward, pressure switch at pump turns it off.29 Encase float switch in Ziploc bag to keep bugs out of it-- common cause of failure. low-level alarm switch turns on light or audible alarm water drops below specified level. Sand Filter In slow sand filter, water passes through layer of sand from top to bottom. Treatment is biological mechanical. Beneficial bacteria form thick film on surface, as well as film over interior sand particles. Suspended particles catch in this layer, pathogens are eaten by beneficial microscopic organisms. properly made managed sand filter has very high pathogen removal rates. Slow sand filtration is simple, inexpensive technology treatment of water that may have pathogens.31 It is especially appropriate rustic homes, villages, small communities that are required to use filtration to comply new regulations. (See Figure 30: Small Sand Filter, p. 86.) Emergency storage sand filtration can be combined in one big tank. If peak demand filtered water is greater than sand filter yield, then separate tank is needed to cover these peaks (this is usually case). Flow rates in slow sand filters are slow: 1/5-1/3 gallons per hour per square foot of filter surface area (7-11 liters per hour per m2). Multiple Tank Management There are plenty of reasons to have multiple tanks--different kinds of water, specialized treatment or settling functions in particular tanks, emergency water set-asides, or simply that you bought one tank then another. Each of these reasons, in each context, will have its own optimal plumbing layout. using multiple tanks, key to simplified management is to install them so that maximum water level in all tanks is same. This reduces redundancy in inlets, outlets, controls tremendously. (It may not be problem to have floors of different tanks at different levels, provided master tank has lowest floor--see Figure 26, opposite.) At extreme, one tank alone can have master inlet outlet, level indicators, overflows, float valves, etc. etc., any number of other tanks plumbed to bottom of it combined inlet/outlets. water level rises in master tank, water will flow to others. it drops, it will flow back. water reaches overflow in master tank, others will stop filling simply because level in master tank stops rising. Besides combined inlet/outlet at bottom, each Ïslave" tank only needs access, drain, screened vent. Freeze Protection Water has high specific heat. It absorbs great quantities of heat stores it long time. It reacts slowly to temperature variations. It takes lot of time energy to heat water, it must lose lot of heat energy before it freezes. In climates wide daily temperature swings, tank of water can keep itself from freezing by virtue of its thermal mass alone. Besides obvious benefits of keeping water from freezing solid, there can be advantage to keeping stored water warm. If water is to be used indoors, warmer incoming water reduces heating load both building hot water heater. Following is inventory of methods to provide freeze protection stored water Some can be mixed matched; others are mutually exclusive. As always, passive methods (listed first) are cheaper more reliable. really extreme cold, you will want to research other techniques.32 Place tank in warm microclimate, exposed to southwest (to heat it up before nightfall), windbreak shelter to north. Bury inlet outlet plumbing below frost line along bottom couple feet of tank (see photos, below). Position inlet outlet plumbing on sunny, sheltered side of tank insulate it, especially above earth's surface. Insulate tank strawbales, sawdust, or, if underground, pumice, perlite, vermiculite, or blue foam foundation insulation. Increase solar gain of exposed tank by painting south side black. Cover south side of tank glass to make it low-temperature solar heater. Shield tank high thermal mass material such as stone, brick, or adobe (most effective in climates large daily swings in temperature). Bury tank, or build berm (earth mound) around it, to take advantage of heat insulation from earth. Maintain sufficient flow through system to keep water from freezing. incoming water from spring or well may not seem warm swimming, but in freezing conditions it is warmer than water in tank. Use thermostatically controlled valve or switch to set water circulating temperature drops below set point, or use recirculating pump to continuously circulate water through system. Circulate water from above ground tank into buried tank or pipe to draw heat out of earth send it back to tank. Use in-tank electric immersion heater. Place tank in enclosed /or heated space. Drain vulnerable parts or entire system winter. Chapter 6: Emergency Storage Storage emergency supply can come from: secure reserve in your regular tank reservoirs of water in your house plumbing alternative sources in your surroundings long-term storage in sealed containers After considering how much water you need, we'll run through these options, then look at how to protect stored water, finally, water storage considerations fighting fires. How Much Emergency Water Do You Need? drinking cooking, two liters per day per person is reasonable figure. fanatical conservation, all other uses except clothes washing can be met five gallons day (20 L) of water, or even less. Clothes washing is resistant to conservation--it will probably take as much water as everything else combined. Since any old water will do clothes washing, you're better off planning on going to river laundry than storing water. (If you find yourself suddenly constrained to this level of water consumption by disaster, you can take solace in fact that this is about how much water humans have lived on in most areas all of history, including most people today.) How long time period to store water is another question. How long do you expect water could be off? most contexts, week to month's worth of water is reasonable amount. In some places distinct dry season, it may make sense to have enough stored water to make it through dry season, even if it is eight months long. Emergency Storage You Already Have regular storage in your water system can serve well as emergency storage, especially if you pay attention to water security suggestions in next section elsewhere. (Plumb your tank emergency reserve, Figures 16, 29, make your tank structurally sound, Appendix B, etc.) advantage of using your regular water storage emergencies is that it is maintained automatically as consequence of regular maintenance of your system. Chances are that bit of resourcefulness will turn up considerable amount of alternative water supplies also, example: Water in your plumbing: Open highest tap collect water from lowest. Ice cubes in freezer. Water in toilet tank (not bowl!) is worth saving using. You can unhook flush valve to keep someone from flushing away this suddenly valuable resource. hot water tank is substantial reserve of usable water. It can be accessed through drain valve at bottom. water may come out calcium deposits in it, can be allowed to settle out before use. Hot water tanks should be secured metal straps so they don't tip over in earthquake. Rooftop solar heaters can yield emergency water, too, especially if they are of storage type. If plumbing in house is thrashed, you could shut off service shut-off valves to keep water from leaking out of solar heaters. Usually there will be service shut-off valves on both incoming outgoing lines. Hot tubs, pools, decorative ponds contain large amount of water suitable washing, bathing firefighting. Nearby surface water: If you have water source nearby such as natural watercourse or reservoir, you could supplement your emergency stored water water carried from that source by hand, wheelbarrow, bike cart, car, or truck. You are fortunate if you are surrounded water that is naturally drinkable. But, as billions of people worldwide are aware, even quite funky water serves fine most uses (see Table 1, Different Water Qualities Different Uses, p. 7). Rainwater collected directly from sky into bowls is OK to drink directly virtually everywhere. Rainwater collected from roofs can have pathogens from rooftop critters such as rats, raccoons monkeys. Rainwater is exceptionally well suited to use washing, dishwashing, bathing. Nearby groundwater: Indigenous people, forced to find water in your suburb, might tap into abundant, fairly clean supply accessible via shallow hand-dug well in nearby creek bank. Your well: You can hand-pump small quantities of water from well using bought or improvised hand pump: Plunge length of pipe check valve on bottom up down in casing, as if you were churning butter, water will come out top. Long-Term Storage in Small Containers It is wise to supplement other emergency water supplies drinking water stored in small containers. shelf life of emergency drinking water depends on its original quality, material it is stored in, amount of light it is exposed to, storage temperature. Water stored in aquifers millions of years is fine. Water in human-made containers can be rendered unpleasant or useless drinking by: container breaking chemicals from container leaching into water permeation of outside chemicals through container walls into water bacterial regrowth algae growth Well-washed glass jugs, plastic screw-top milk jugs, water bottles, etc., are good vessels emergency water. Water stored in glass is at risk of loss via breakage. Water stored in HDPE plastic several years is pretty much assured of having barely tolerable plastic taste. Other plastics leach things that are nastier but taste less. You can cover your bets by using mixture of container materials: bunch of glass jugs, 55 gal (200 L) HDPE drum, some polycarbonate PETE plastic containers. 55 gal HDPE plastic drums are classic, ubiquitous liquid storage container. They are ideal storage of bulk emergency drinking water-- they have contained something non-toxic. Lightweight enough to carry up into apartment empty, these drums are still movable (just barely) full. They are tough resilient. One 55 gal drum holds drinking water family of four three weeks. Food grade steel drums are possibility but much less desirable due to their tendency to corrode leak. Municipal tap water in developed countries is reliably pathogen-free requires no treatment before storage. If you doubt your well or spring water, you can add 16 drops of chlorine per gallon before storing it. Ozonation should also work. Label all containers date, water source, method of disinfection used. Store your containers in dark, cool place. In few years, sample water see what is working your source water, storage conditions, taste. You can then store proportionally more water by these means. If these filled containers are exposed to any light, they may grow algae. Even if it produces strong taste, it shouldn't be harmful to drink. Protecting Stored Water In Hazards of Stored Water (p. 52) we considered what harm stored water could do. Now we're going to consider what harm can be done to stored water how to avoid it. (Note: freeze protection see p. 74.) Earthquake-Resistant Storage In designing earthquake resistance, it is important to recall that: Inlet or outlet pipes are as or more likely to break than tank itself. Raised storage, in towers or rooftops, is much more likely to fail in earthquake. Properly engineered storage is much less likely to fail. Earthquakes can generate variety of motions. Earth can move back forth, or up down. rhythmic nature of movement can result in extreme amplification if it coincides resonant frequency of sloshing water in tank. most violent motions earth can generate are all but impossible to engineer structures . Accelerations of 1-2 gravities have been recorded. Many building codes call structures to resist acceleration equal to 0.2 gravities. Imagine plane of earth tilting until flat ground tank was sitting on is now sloped 20%. Would tank fall or slide over? Perhaps it needs to be anchored. Fire-Resistant Storage In fire, most likely failure points water storage system are pieces that can burn. most secure installation would not have plastic outlet pipe, rubber seals or couplings, wooden supports, delicate steel supports surrounded by fuel, or depend on unprotected electronic controls. Even steel members aren't next to water but are next to trees or brush can heat up to point that they melt. Water inside tank can carry heat away, perhaps enough to save walls from burning. In wildfire sides of one old redwood water tank nearby burned down to water level, burning stopped. residents couldn't get new water into tank, however, because wooden trusswork that supported galvanized inlet line burned away, unsupported pipe broke. Hurricane-Resistant Storage Tanks are most vulnerable to wind they are empty or nearly so. full water tank, made of any material, is so heavy it is not likely to be affected by wind, except indirectly by damage from flying debris or falling trees puncturing side or breaking outlet. Lightweight tanks definitely need to be anchored against high winds in areas that experience them. Lightning Grounding Steel tank installations without cathodic protection need to be grounded in accordance local electrical fire codes. Use zinc grounding rod tank touches earth, not copper rod. Roots Trees Probing, swelling roots, swaying branches, falling trees can wreak havoc on water systems. One of sadder but necessary maintenance tasks is to rip out tree seedlings that are too close to tanks. Toxic Leakage or Leaching Water stored in aquifers can be threatened by toxins from underground gasoline storage tanks, dry cleaners, agricultural poisons nitrates, or salt water intrusion driven by over-pumping (see Aquifers, p. 16). Water stored in tanks is pretty much immune to contamination of this sort from outside; concerns are contamination of source water, leaching from tank (see How Water Quality Changes in Storage, p. 9, Tank Materials, p. 39). Hazard of Permeation Permeation is diffusion of chemicals through wall of container or pipe into water. Permeation can be issue aromatic toxins (gasoline, kerosene, pesticides, like) plastic pipes or containers. example, if you store emergency water in polyethylene containers (such as milk jugs) next to gasoline cans, fumes leaking out gas can's lid can permeate through plastic contaminate water. municipal PVC water main passing through toxic waste plume can absorb industrial toxins by same route. Permeation of toxins can be avoided by using impervious material to contain water (metal, glass) or (better yet) keeping toxins well away from water. Thick-walled polyethylene containers (such as 55 gal drums) are significantly less permeable than thin-walled ones (such as milk jugs). Armed Marauders If you are worried about hordes of barbarians stealing your water after disaster, your best bet is to hide it underground, or disguise it (e.g., as ferrocement boulder). Children, Vandals, Unauthorized Access One desert community know occasionally found passing motorists skinny-dipping inside their potable water tanks. Fences locks provide some security against this sort of thing. You can remove valve handles, lock valves in position, or enclose them in locked valve boxes to reduce chance of accidental or malicious adjustments. IT Publications has this to say about children water systems: ÏChildren should be considered to be compulsive saboteurs of system. Although they do not do so deliberately, their curiosity leads to much damage repetition of work. Open pipe ends, exposed pipeline, fresh masonry all will attract attention, frustrating results."16 Systems Firefighting One of most valuable uses stored water is to put out fires, saving people property. In places fire safety is issue, fire requirements (legally mandated or owner preference) often drive design, setting much higher standards amount of storage, pipe sizes, pressure. There may also be fire department requirements road width, grade, paving huge turnaround at your house. It might be cheaper to go beyond water system requirements (even as expensive as plumbing is) in trade some slack on road access requirements, if fire marshal is willing. In most fire emergency situations, flow demand is so much greater than supply that storage is essential to cover it. example, incoming supply might be 10 gpm, while fire department can go through several thousand gallons in fifteen minutes.m However, incoming supply water may also make crucial difference in reality--especially if reality is that your tanks are low to start , or get drained wetting things down before fire even gets there. Armoring supply system, as described in Fire-Resistant Storage (p. 77), will increase likelihood that at least some water is being added to system even as you are rapidly draining it. If you don't have entirely gravity-powered system, should you use electric pump, gas pump, or generator electric pump? Like everything else, it depends on context. live firestorms are so extreme that scenario of staying fighting fire isn't realistic, we're not planning it. Our plan is to hose place down before fire gets here get out. At that time, electrical grid is likely to be functional, so electric pump makes sense. In general, prefer fire emergency hardware, especially pumps, incorporated into regular system. plan to use fire emergency pump to pressurize rainwater supply to our house. Besides efficiency of item doing double duty, it's much more likely to work fire comes if it is something that is regularly used. plumbing your pool or spa, hook things up so that you can use pool's own filter pump to power fire hose. Some people also include gas pump in pool plumbing firefighting. This may require different-sized lines /or pump adequate flow pressure. Make sure supply comes from near bottom of pool, so system can access most of water. If you use gas pump irrigation, you might as well use it fire, too. Likewise generator. most versatile foolproof setup is electric pumps backup power, batteries or generator. Water elements fire safety are of three classes: systems to support hoses manned by people, automatic fire sprinklers (interior exterior), water to refill fire trucks: Water Fire Hoses To operate fire hoses, you will need: Stored water gravity pressure decent-sized line. instance, high-pressurem 2" line would supply two 1.5" hoses at same time. Fire hoses stored on-site, convenient to hydrants. pump to make up low pressure /or inadequately sized line. foam injection system (see Foam, p. 81). Even one big, high-pressure fire hose places extreme demand on system hardware. Accommodating this demand can easily double resources required to build your storage distribution plumbing--all something that probably never will get used. Is it worth it? It is form of insurance, one that you'll have to judge how much is enough. difference between 3/4" garden hose 1-1/2" fire hose is truly phenomenal. Likewise difference between 40 100 psi of water pressure. You'll need powerful water delivery capability to have chance against considerable power of house fire or wildfire. we are burning brush piles, occasionally gust of wind suddenly drives flames skyward on windrow of fifty truckloads of tinder-dry brush. moment's burst from 1-1/2" fire hose ( 60 psi of pressure) puts it right down. garden hose going full-blast would do essentially nothing; it would just take bit longer it to get so hot that you had to back off. If we were to let whole thing get fully engaged roaring, wall-to-wall two-story-high flames, we could probably put it completely out in few minutes fire hose. On other hand, fully engaged firestorm in Southern California chaparral, whipped by freeway-speed, hot, dry wind is beyond capability of any fire hose to suppress. This is you simply run your life ( hope that your homeowner's insurance is paid up). Some other things to think about are location of fire hose standpipes (small hydrants), how they are plumbed. hydrants should be near structures, but not so near that it would be too hot to hook up hoses if structure were burning. plumbing needs to be secure. 've seen hydrants that were made by connecting hip-high vertical length of steel pipe directly to tee in underground PVC pipe. Imagine panicked person pulling hard bit more hose they desperately need to keep their home from burning down. Pulling, that is, on steel lever brittle connection to delicate plastic pipe. If it breaks, they've got tough decision--turn off water, or watch tank empty uselessly, in each case while house burns. One solution is to encase steel in enough concrete at ground level so that steel will bend before plastic underneath breaks. better solution is to put two ninety-degree bends at right angles, so standpipe can be pulled or knocked over without stressing plastic pipe (see Figure 27, at right). Water Fire Sprinklers Water system features fire sprinklers: Stored water gravity pressure line size engineered to supply sprinkler system, possibly pressure booster pump. Line sizes residence range from about 3/4" at 100 psi to 1-1/2" at 40 psi.m Roof-wetting systems could be designed to Ïdrool" water onto roof at lower pressure. mechanism triggering sprinklers at right time, such as heat-sensitive sprinkler heads. Roof-wetting systems on home roof-rainwater harvesting system can be plumbed to recycle water running down gutters, so it takes longer to run tank dry. Indoor fire sprinklers may or may not stop fire, but they will almost certainly slow cool it enough so residents can escape. Sprinklers dramatically increase survival odds in fire.33 There is detailed code interior fire sprinklers. exterior sprinklers--designed to keep wildfire from catching your home on fire-- design is up to you. common roof-wetting design is high-pressure irrigation sprinkler or two. Here's idea rooftop sprinkler design that like: Place copper pipes along high points of roof, small holes drilled in them water to jet (or drool) out. 've not yet built one of these, but it seems that water would get used much more efficiently, that you'd cover whole roof even if pressure were really low (as it will be if your neighbors are all wetting things down in panic). What's more, if you've got roof rainwater harvesting system, water would virtually all go back into your tank from gutters, so you could just turn pump on leave water to circulate. same type of system (pipe holes) could be installed under eaves to protect them as well, although it wouldn't recycle. If you try one of these, let me know how it turns out. Water Fire Trucks Big fire trucks actually don't carry that much water--usually no more than 800 gal (3 m3). Dedicated tanker trucks can carry few thousand gallons (10-15 m3). Sources refilling trucks include: Stored water gravity pressure, large diameter line, right fire hose fitting to rapidly refill fire truck. One solution could be 4" hydrant right by tank. very little pressure, it can rapidly deliver water to truck. Fire trucks pumping water out of bodies of water, such as ponds, swimming pool, hot tub, or river--if they have suction hose or portable pump. Foam Injecting Type firefighting foam or gel greatly increases effectiveness of water fighting fires. wet foam sticks, smothering fire on something burning, or insulating reflecting heat from something you're trying to keep from catching fire. If your plan is to wet things down run your life, foam is much, much more effective than water alone. Instead of running off like water, it stays. Turn your house into big marshmallow go. neighbor of ours did this his house, including big wooden deck. He watched flames cavitate under deck, but it didn't catch fire--pretty impressive. Chapter 7: Examples of Water Storage Systems Different Contexts Poor Surface Water Quality, Limited Groundwater Context: community of 100 in arid Southern California desert. Goals: Provide conservative residential use 30 homes, maximum use of 300 gpd (1.1 m3/day) per household. Provide substantial fire safety reserve. first seventy years, economy owner-serviceability were primary goals. Owners have recently, reluctantly decided to trade off economy, owner-serviceability, environmental impact in order to meet requirements of Surface Water Treatment Rule34,35 minimize possible liability exposure. Water supply: Gravity flow springs (5-17 gpm/20-60 lpm diverted from 8-30 gpm/30-115 lpm flow) turbidity legal challenges, well from aquifer nitrate levels hovering just below legal limit (14 gpm/53 lpm, 12 hrs/day max pumping); some harvesting of rooftop rainwater runoff. Storage: Small aquifer ( capacity of approximately one or two years consumption), three tanks (two 50,000 gal/190 m3 tanks, one 3000 gal/11 m3 tank), about 10,000 gal (38 m3) in three private rainwater harvesting tanks. Average use: 4500 gpd. Peak use: 9000 gpd up to 20 consecutive days of really hot weather. Fire design flow: System can deliver 100,000 gal (380 m3) at 35 psi (240 kPa) to 6" hydrant. It can also power one or two 1-1/2" fire hoses on distribution network, is 2" pipe, pressures from 38 to 100 psi depending on elevation.There are about 40,000 gal (150 m3) of emergency set-aside that can only be accessed by opening valve at tanks. This is not ideal; it should also be directly connected to hydrants. Water security: Good. There is sufficient storage to meet two weeks' use without water income. In absence of electricity, this system can deliver clean (if not legally compliant) spring water equal to half peak dry season consumption. In case of flood waters contaminating springs or washing out pipes, it can deliver well water equal to full rainy season consumption. There is concern about falling water tables due to overdraft all around, but this has not hit springs nor this well directly as yet. (Except that groundwater level was lowered due to overdrafting well during five years springs were off-line while code-compliant treatment was being installed.) Issues notes: This system is above ten-connection threshold is thus subject to draconian provisions of Surface Water Quality Act. spring water is substantially pre-treated in tank first. settling ozonation, system delivers coliform-free water < 1 NTU turbidity at up to 5 gpm, meets sky-high performance requirement of law. Nonetheless, package treatment plant, on-line turbidimeter, chlorine injector, online confirmation of chlorination meter are being added to comply proscriptive requirements of law. This law is classic example of tunnel vision (see p. 5). Hopefully law will be made more flexible in future. Allowing users to meet performance or proscriptive requirement (as is case building codes) would be great improvement. Only Stored Water in Dry Season, Hydroelectric in Wet Season Context: Ecovillage events center of 30 residents in Highland Central Mexico. Goals: Provide storage highly conservative residential use ten homes, dry season max use of 106 gal (0.4 m3) per day per household. Low cost, low impact, simplicity are paramount. Water quality goal is <10 fecal coliforms per 100 ml.4 Fire safety would be great but is beyond means of owners. Water supply: Rainfall runoff, during four- to six-month rainy season only. During dry season all water used is drawn from storage, storage level drops each day. There is community water diversion at base of waterfall that runs primarily during rain, at zero to 265 gpm (1 m3/min). Every home harvests its rooftop rainwater. In pinch people can buy tanker trucks of water driven up from valley 500 m below. Storage: There is rock dam spanning two vertical veins of bedrock, forms community tank of 100,000 gal (375 m3). smaller rock dam forms waterfall diversion settling pool of 11,600 gal (44 m3). There is ferrocement distribution tank of 2600 gal (10 m3) used to meter water (by tankful) as it is transferred from big community tank to about twenty private tanks of ferrocement, rock, cement, or plastic, altogether hold another 53,000 gal (200 m3). Average use: 600 gpd (2,256 lpd). Peak use: rate is unknown, but peak flow occurs during big festivals hosted at site, hundreds of attendees. Water security: Poor. In absence of electricity, many homes could not get water out of their buried cisterns easily. If monsoon is late, or there is leak, individual homes sometimes whole community run out of water have to have it trucked in. Issues notes: Huehuecoyotl is critical context water storage.They have zero water income six to eight months of dry season. No rain, no creek, no springs, not even reachable groundwater. ( World Bank dug 400' (120m) deep well at village next door, it was dry as dust at bottom.) All their water during dry season is from stored water, of there is less each day.Then, in monsoon it rains 1.5 m (4.5') in four or six months!One interesting thing about this place is that 11,600 gal (44 m3) pool at base of waterfall can be used as hydroelectric storage Ïbattery" during rainy season. That is, draining pool through hydroelectric turbine yields electricity, just like battery.mThere is more on rainwater harvesting seasonal hydroelectric systems at Huehuecoyotl in our forthcoming book, Rainwater Harvesting Runoff Management3. greywater systems are described in Create Oasis Greywater2 Branched Drain Greywater Systems.36 Creek Direct Remote Storage Sand Filtration Context: Rural conference center on thirty acres in Southern Oregon. Goals: Provide conservative residential use up to thirty seasonal workshop participants handful of year-round resident caretakers. Provide irrigation 1/2 acre (2000m2) of gardens orchard. Fire safety is beyond scope of this system. Water supply: Year-round creek (> 30 gpm/110 lpm flow). Storage: System runs creek direct, 300 gal (1.1m3) tank at far end of system. This is intended to cover peak demand flow, supply more secure water to highest, last houses on line, provide reserve diversion washes out system needs air flushed from lines. Average use: 600 gpd (2.2m3). Peak use: 900 gpd (3.3m3) up to 20 consecutive days of really hot weather during workshops. Water security: Good. This system does not use electricity at all. In case of flooding, water is not drinkable, diversion washes out. However, this only happens in winter, population is low, 100 gal (0.3m3) of reserve is sufficient to hold over residents until diversion can be restored. Issues notes: creek water, one branch of comes out of recent clear cut, had higher than desirable coliform bacteria. system was providing less water flow than desired. water line washed out, someone had to go out hours (usually in dark, during freezing rain) de-couple line in several places to let air out before flow would start again. tank was defiling most beautiful place on creek, owners wanted to move it. Finally, highest two buildings on system-- last on line--didn't have as much water security as they'd like; any open valve lower down would leave them high dry. First, bacteria issue. We inventoried all possible drinking water sources, included very small, shallow spring nearby, bigger deeper but distant springs, Ïnaturally" filtered creek water coming out bottom of old dam filled sediment, creek itself. We concluded that no other source was worth making separate delivery system , that best option was to treat creek water itself slow sand filter (Figure 30, at right). Now we're going to look how minor change in storage this system did lot to resolve other issues: water source, creek, flows several times maximum flow capacity of water line. Of 30 gpm (110 lpm) of creek flow, 1" pipe captures about 2/3 (20 gpm (75 lpm)) diverts it into tank. Of that only about 1 gpm (4 lpm) average is consumed, balance overflowing tank. Much of settleable solids stay in tank. These settled solids were likely to be vacuumed into distribution system by combined outlet/ drain. tank was not increasing peak system capacity, not providing reserve, nor improving water quality. So we took it out. This changed system performance as follows: Then caretaker had inspired idea what to do tank--put it at far end of distribution system. Probably only someone little water system design experience could have conceived of such unconventional geometry--usually storage is at beginning of distribution system. suggested putting tank at level such that overflow is 2" (5 cm) lower than creek diversion several hundred pipe feet ( few hundred meters) away on other side of ridge (see Figure 29, previous page). tank inlet/outlet located third of way down, tank fills whenever all valves down below are shut. someone turns on garden sprinkler while someone is in shower, water flows both from creek diversion from upper third of tank, giving bather good chance of getting soap off before flow drops. By adding separate outlet two-thirds of way down, tank provides water pressure supply upper two houses that is not affected by use in rest of complex. outlet reserve at bottom of tank, there is emergency water that can run whole place couple days if line washes out, or so that maintenance can be done at convenient time. Also, pressure from reserve water can be used to push air out of system so that it starts up far less effort. total cost of all changes to system is about $35 two bulkhead fittings to make new outlets on tank, in-line particle filter to ensure that solids from creek don't fill line. following chart shows system performance at end, as compared to beginning--quite illustration of how design of storage can totally change performance of system: System Performance After Moving Tank to Far End of Distribution System Parameter Performance Supply flow 30 gpm 113 lpm Static pressure in system 17 psi 120 kPa 40% more Max flow from system 4.2 gpm continuous/ 8 gpm 15 min 16 lpm/30 lpm 260% more Reserve on system failure 300 gal 1 m3 300 gal more Time to restart system 1/2 hour Daily use 600 gal 2 m3 Water contributing to sediment load, daily 600 gal 2 m3 97% less Very, Very Low Pressure Context: Single-family residence in steep, wild canyon in Southern California. Goals: Provide conservative residential use one family of four, by gravity. Provide irrigation 1/8 acre (500 m2) of gardens orchard. Fire safety is beyond scope of this system. Water supply: Horizontal hard rock well/ infiltration galley ( tunnel water percolating in or out of it), 1-2 gpm flow (4-8 lpm). Storage: kitchen tap shut, shallow pool in floor of infiltration galley rises until it meets overflow. tap open, pool level drops up to 6" (15 cm), to spill point of outlet. Average use: 100 gpd (0.4 m3/day). Peak use: 200 gpd (0.8 m3/day). Water security: Excellent. This system does not require electricity has only short run of pipe. Floods affect neither pipe nor well. It is thus quite secure. Falling groundwater is about only thing that could threaten this water supply. Issues notes: This system runs off of almost no pressure. Simple Jungle Eden Context: community of twenty, 45 minutes' walk into jungle from Caribbean coast of Costa Rica. Goals: Provide conservative residential use five families. Irrigation is all directly by rainfall. Fire safety is not issue. Water supply: Creek of about 5-30 gpm (20-110 lpm) is used directly drinking, clothes washing, bathing (no soap). Small amounts of water are hand-carried into homes. Storage: storage is in soil aquifers that supply creek, plus few gallons in small containers in homes. Average use: 100 gpd (0.4 m3/day). Peak use: 200 gpd (0.8 m3/day). Water security: OK. This system is only affected by extensive runoff during high water, lowering quality. Issues notes: This system has no artificial plumbing at all. Rural House Well Context: Single-family residence in Arizona desert. Goals: Provide conservative residential use one family of four, plus irrigation of 1/2 acre. Wildfire safety is not major issue due to low fuel load in surrounding desert. Water supply: 400' (120 m) well, safe yield of 200-1000 gpd (0.8-3.8 m3/day). Water level varies between 190 230 feet (60-70 m) below surface. tank is 90' (30 m) above that. Storage: storage is in aquifer that supplies well, in one 2000 gal (7.6 m3) tank. Average use: 200 gpd (0.8 m3/day). Peak use: 400 gpd (1.6 m3/day). Water security: Poor. This system is critically dependent on electricity. Without electricity to power pump, there will be no water in five or ten days. aquifer is being lowered by overdraft from neighboring wells, at some point well could go dry. Issues notes: would feel better about water security in this spot addition of rainwater harvesting system its associated storage, perhaps second tank well water also, plumbed so that it is all reserve. Urban Apartment Context: Apartment in New York City. Goals: Provide conservative residential use one family of four. Fire safety is provided by municipal building systems. Water supply: Municipal water meter. Storage: municipal water system has various reservoirs, but relies primarily on regular rainfall, is typical in this climate. building has 10,000 gal (38 m3) tank on roof, supplies approximately 100 people in building.There is emergency on-site storage of filtered drinking water in several one gallon HDPE screw-top milk jugs, glass apple juice jugs, 5 gallon polycarbonate jug, plus 30 gallons in hot water heater four gallons in toilet tank. If push came to shove, there are 30 gallons in freshwater aquarium. Average use: 150 gpd (0.6 m3/day). Peak use: 300 gpd (1.1 m3/day). Water security: OK. This system is critically dependent on electricity. There is small rooftop tank, but without electricity, there will be no water in few hours at most. Issues notes: would feel better about water security in this spot addition of 55 gallon drum of clean stored water. Swank Suburban House Context: 5000 ft2 (460 m2) single-family home in new gated community on outskirts of Los Angeles, at wildland/ urban interface. Home is bordered by mountainous dry scrub on upwind side. Goals: Provide extravagant residential use one family of four. Supplement fire safety provided by municipal system to extent practical. Water supply: Municipal water meter, water from Colorado River Owen's Valley. Storage: municipal water system has various reservoirs, but primary water sources are hundreds of miles away. local reservoirs require electricity to get to this location are of questionable earthquake-hardiness. There is hardly enough local water to meet residents' drinking needs. home has 30,000 gal (113 m3) swimming pool.There is emergency on-site storage of filtered drinking water in several one gallon jugs, plus 50 gallons in hot water heater sixteen gallons in four toilet tanks. Average use: 1000 gpd (3.8 m3/day). Peak use: 2000 gpd (7.6 m3/day). Water security: Poor. This system is critically dependent on electricity, very long, weak supply line. Without electricity, there is no water immediately. greatest vulnerability, however, is of large earthquake damaging major portions of supply system. At this location, people could potentially be entirely without water months. If earthquake precipitated economic crisis, this house could be without water indefinitely. Issues suggestions: pool does quite lot to improve water security at this spot. It could be further improved addition of few 55 gallon drums of drinking water.Fire safety would be improved addition of pump fire sprinklers /or hoses. Appendix : Measurements Conversions How units are dealt in this book: Any measurement clearly expressible without numbers or units is expressed without them (e.g., Ï arm's length"). text flow is too chopped up by non-essential numbers, they are relegated to footnotes. skipped metric conversions of pipe sizes in text. They are all here. Measurements examples or construction plans are expressed in national units think most tanks of this type will be made. If units are approximations or don't really matter, units are given to nearest round number. Thus, photo of tank might be captioned Ï10,000 gal (40 m3) tank" rather than Ï10,000 gal (37.854 m3) tank." Using tables: Everything in same row is equal. example 1'=12"=0.3 m=30 cm. Appendix B: Tank Loads Structural Considerations This section gets bit technical. If this puts you off, not to worry--just skip it (if you're not building tank or building one under 1000 gal/3.8m3); or skim it, glean what you do from it (if you're building tank up to 30,000 gal/113m3.) If you're building bigger tank, hire engineer experienced contractor. Forces on Tanks tank has to resist variety of forces structurally: Water pressure: acts at right angles to every surface--pushing down on floor, out on walls, up on roof (if roof space is filled water). Water pressure is directly proportional to depth alone. If you are building your own storage water column deeper than six feet, be careful. water deeper than eight feet, you should have engineer involved design. (See also Hoop Stress, next page.) Point loads: These include people walking on roof floor, rocks poking into underside of floor, cars running into side, kids ice picks, yahoos using your tank target practice÷ Earthquake loads: These can topple tank onto its side, or slide it sideways off footing, knock over water towers, or simply shake bejeebers out of tank until sides split open. Wind loads: These can blow over empty tank or (in case of very high winds) spear it flying debris or crush it falling trees. Gravity loads: If tank is supported unevenly, floor can crack or sides split under strain. This can happen if earth under tank settles unevenly, is washed out from under tank by water, turns to squishy muck, or heaves frost or big roots. Ice loads: If thick ice forms on water surface inside tank, then water level falls, ladders interior pipes can be ripped right out of tank walls. If pipes, fittings, or whole tank freezes solid, they can split open. Soil loads: Buried tanks can be subjected to intense inward /or upward pressures (see Buried Storage, p. 31). flexible floor, stiff floor, cylindrical walls, domed roof all work totally differently structurally: All flexible floor has to do is not puncture or tear. earth (or gravel on top of earth) supports flexible floor. Providing it is flexible enough to conform to whatever degree of unevenness is present in supporting ground, force on it is minimal. It is not being stretched, bent, or sheared, just gently compressed between water earth. How gently? floor of 8' deep (2.4 m) tank is pressed down just 4 psi (28 kPa), earth presses back equal amount. Saran wrap could probably resist this force. stiff floor, on other hand, can develop tremendous bending forces if it is supported unevenly. If portion of floor of big tank is cantilevered out over wet, squishy soil is doing nothing to support tank, it is up to floor to resist many tons of water that is trying to crack concrete slab. Ironically, 8" thick (20 cm), steel-reinforced concrete slab might fail in this circumstance, while thin, flexible pond membrane probably would stretch to conform to new shape be fine.If you make stiff floor, you've got to also make it really strong. One way to make floor stronger is to give it conical or dish shape (see shape discussion, below, sidebar Tempting Floor Shape Innovations, P. 112). Cylindrical walls are placed in tension (pulling) by water pressure. Walls of bought tank will be fine, as manufacturer engineers them your installation won't change loading (unless overflow plugs, causing tank to be pressurized like one that is about to explode in Figure 32). There is more on designing your own walls under Hoop Stress, below. domed roof takes advantage of fact that materials are much stronger in compression (squeezing) than in bending. People walking on flat roof stress it through bending, while domed roof supports people walking on it mostly in compression. domed shape uses strength of material to best advantage, as most materials are much stronger in compression than bending. conical roof (or floor) resists loads in combination of bending compression. Hoop Stress ÏHoop stress" is term loading on cylinder is being pushed out evenly in all directions from inside. This push tries to stretch cylinder walls in tension. This is dominant way tank walls are loaded, by water pressure from inside. Ïhoop stress" on tank walls under pressure is proportional to depth of water diameter of tank. : is hoop stress p is water pressure r is tank radius t is wall thickness If you are building tank, you must consider wall forces, size tension members of lower wall to withstand applied forces safety factor of at least two. If walls are free to move at bottom, they will be loaded in pure tension by outward water pressure (that is, water will be trying to stretch wall apart). Plastic steel do very well resisting loads in pure tension. In fact, plastic, is not especially strong material, can withstand thousands of pounds of tension in water tank. In redwood tank, hoop stress is taken entirely by hoops. hoop vertical spacing is adjusted so all hoops are equally loaded (see photo, p. 45). Because walls in redwood tank are free to move away from floor slightly hoops are stressed, there is no shear between floor walls, force is just as in this ideal equation. If walls are rigidly attached to floor, loading at bottom is combination of tension, bending shear ( latter concentrated at wall-to-floor joint). This requires extra reinforcement in case of rigid materials such as steel or ferrocement. (Plastic just stretches tiny bit extra until shear is negligible it is mostly in tension.) In ferrocement tank, walls can't shift away from floor. They bend, putting shear stress in material but reducing hoop stress. Also, lath hardware cloth prevent even fine cracks in plaster, so plaster actually can ( does) carry quite bit of tension load. Because of these factors rebar spacing does not have to be as close as if it were taking 100% of tension load. There are three strategies to strengthen base of walls wall-to-floor joint in ferrocement tank: Increase rebar spacing size near bottom of wall. Increase thickness of wall near bottom. (Using fatter rebar automatically increases thickness of plaster inside armature, plasterers can be instructed to make coverage thicker near bottom.) Fatten joint between floor wall inside out fillet (narrow strip) of plaster. Doubling depth doubles stress; doubling diameter does same. Hoop stresses on tanks of 10,000 gal (38 m3) more are considerable; do not skimp on reinforcement in home-built tank. Figure 43, p. 114, shows rebar spacing different depth tanks. Our Tank Calculator gives hoop stress values any size tank.6 Effect of Size Shape Size matters. forces on big tanks are tremendously greater. 1000 gal (3.8 m3) tank can be built totally seat-of- -pants by anyone. Medium sized tanks (10,000 gal/38 m3) require some head scratching. Large tanks (over 30,000 gal/110 m3) should be professionally engineered. Not only are forces greater, consequences of failure are greater, too. was asked to design 100,000 gal (380 m3) tank in steep, narrow valley in highland central Mexico. tank would be located in active earthquake zone short distance from Popocatepetl, active volcano. If it were to fail catastrophically, resulting tidal wave would obliterate at least nearest house, possibly kill several people. Fortunately, was able to instead help community conserve enough water that tank was not necessary. Smaller things act much stronger because loads on bigger things are proportionally bigger. Thus, small diameter polyethylene pipe can contain column of water hundred feet deep (30 m), while big polyethylene tank can't be much taller than person before pressure bursts it. Shape matters. shape determines how material will resist applied force thus how easy it will be to resist given load. example, snow load bends flat roof but puts material in domed roof under compression. membrane roof would stretch concave, under tension. Here are some general guidelines thinking about how shape affects structural integrity: Compound curves are inherently strongest, as in dome or sphere. Simple curves are strong, as in cylindrical tank walls. Folded planes are stronger than flat planes, as in cone, or peaked roof compared to flat roof, or corrugated compared to flat sheet steel. Triangles are stronger than straight pieces, as in roof truss compared to beam. Thicker, taller pieces are stronger than thin or flat pieces in bending. load on wide, flat piece of wood will bend it much more than it would bend same piece stood on edge. Uniformly stressed structures are stronger. wall that tapers towards top flares towards bottom is stressed evenly, as there is more material there is more stress. It would thus be harder to snap wall off its footing than if it had uniform thickness throughout, in case all stress concentrates at bottom. Shorter spans are much stronger. example, flat roof that is supported by central pillar is four times stronger than one that spans whole diameter of tank without interior support. Shapes that enclose more volume same amount of material are stronger, up to point. example, tube is stronger than solid rod, bigger, thinner-walled tube is stronger than smaller, thicker-walled tube. This holds true until walls are so thin they buckle. Note: This is true compression, bending twisting, but not tension. tension, shape doesn't matter, only amount of material. Appendix C: More About Plastics This is supplemental information on health environmental issues plastics used water containers, storage, or plumbing. more basic information details on most commonly used materials can be found under Tank Materials/ Plastic, p. 45, in Table 7: Tank Materials, p. 40. If you really want to get into it, you can download research notes behind this section.6 These consist of pages pages of abstracts of studies web links on leaching from all materials (not just plastics), permeation, disinfection by-products, bacterial regrowth. This section is organized roughly from most to least recommended material. name is followed by plastic's abbreviation recycling code number, common uses, recommended uses recyclability. Biologically Based Polymers Hopefully in future, there will be water storage plumbing components made of bio-based polymers, but 'm unaware of any available now. High Density Polyethylene (HDPE #2) HDPE is preferred plastic water tanks, it is most commonly used material. It is relatively innocuous in its manufacturing, use, disposal, at least compared to other plastics. (See Tank Materials/HDPE , p. 46 more info.) Low-Density Polyethylene (LDPE #4) Used in food storage bags some Ïsoft" bottles. From health ecological standpoint it is same as HDPE (above). Polypropylene (PP #5) Used in rigid containers, including some baby bottles, some cups bowls. Comparable to HDPE in health environmental pedigree. Polyethylene Terephthalate (PETE/PET #1) Used most clear beverage bottles. best combination of good taste, shatter-resistance, light weight acceptable environmental health issues small, portable water bottles of 1 gallon or less. Ethylene Propylene Diene Monomer (EPDM) EPDM is commonly used pond liners. It is synthetic rubber resistant to heat, ozone, UV light. It is able to stretch quite bit without tearing. There is little data on leaching of EPDM, although it is generally considered to be pretty inert. It is considered more environmentally friendly building material than PVC. (See Tank Materials/ EPDM, p. 46 more info.) Polyamide Epoxy There is evidence that epoxy coatings leach various toxic additives into water. observed leaching decreases exponentially over time. Polycarbonate/ Lexan (PC #7-other) Used in 5 gallon water bottles, some baby bottles, some metal can linings, popular NalgeneÐ backpacker's water bottles. Valued its high strength fact that it doesn't impart taste to water. Unfortunately, polycarbonate can release its primary building block, bisphenol- , suspected hormone disrupter, into liquids foods. This leaching worsens as material ages degrades. Acrylonitrile Butiadene Styrene (ABS) Not used water tanks, or potable water plumbing. It is used drain plumbing, occasionally do-it-yourselfers will incorporate it in water supply systems. manufacture of ABS generates hazardous materials, including carcinogens. ABS is difficult to recycle, is considered only marginally better than PVC (see below) in terms of environment health effects. Cross-linked polyethylene (PEX) Cross-linking makes PEX more durable than HDPE. There is concern that it leaches MTBE benzene into water, also that pipes may prematurely decay rupture, releasing flammable material that would allow fire to quickly spread through building. PEX should not be exposed to sunlight. Fiberglass (Glass Fiber-Reinforced Polyester, GRP) Fiberglass tanks are very strong, lightweight, non-corrosive. Fiberglass is quite bit stronger more expensive than HDPE generally considered to be higher quality. It is certainly superior to HDPE underground tanks due to its high strength. Exceptionally nasty solvents are used in resin used to make fiberglass. literature is strangely silent on its health effects, but 'd be nervous about leaching of residual solvents. Polyvinyl Chloride (PVC or V, #3) Used in water bed bladders other flexible liners, some soft bottles, food cling wraps, rigid pipe. manufacturing installation impacts of PVC are so bad there is serious discussion of banning it. However, rigid PVC does seems to take break from wreaking major environmental health damage while it is in service. Rigid PVC in shade does not seem to leach much into water (but see discussion of issues flexible PVC PVC in sunlight, p. 39). it is time to dispose of PVC things get ugly again. It is possible to eliminate PVC piping, using copper, brass, galvanized, or polyethylene instead. Plumbers are universally adapted to using PVC tank plumbing details, while HDPE requires invention or learning of new techniques. hope that future editions of this book will show fewer PVC details more of other types.