slow sand filter

[markgrossman]

page 86 of your water storage book explained a sweet little sand and gravel filter. seems so simple and natural. thank you a million for enlightening me to this simple technology.

our community, in the mountains of oaxaca, has spring water piped to the community. the spring is about 50 miles away, high up in the mountains, and comes to us by canal. at the entrance to our little village, high up, the water goes thru a 3 stage filter, consisting of 3 cement tanks which each hold approx. 4 cubic meters. the top tank has only a screen to filter out large sediment, the middle and lower tanks are sand. from here the water goes to a large cement cistern of approx. 500 cubic meters. the problem i have is here, there is no top on this cistern, only an open hatch, i put a top on the hatch twice and the locals have removed it, they have a strange reason for this, and as far as i get is this "my grandfather did not have one, why do i?"

so i want to provide more security for my family and hopefully make my neighbors aware of other options..

i read your link here (http://www.oasisdesign.net/water/treatm ... filter.htm)
and still have some questions..only a few questions..

you said a 44 gallon drum will work. this drum is 86 cm high. your article refers to the layer of standing water on top of the sand as such "A minimum depth of .5 m up to 1.5 m is most commonly used" and also states in reference to the sand " minimum of .8m on smaller filters" so, there is a negative space available for the filter. it seems like you need a min. of 1.3 m plus some gravel below. i could have 2 drums welded together, but would prefer something more simple and easier for everyone to build. i would really prefer the 120 liter recycled plastic drum, these are available everywhere and will not rust.

if i went with a 55 gallon drum or if possible the 120 liter drum... could you elabotare more on this system. directly in reference to the levels in cm.

also, i would gladly buy the "centre for alternative technology" packet on water information pack, they state info included on slow sand filter, but i am not sure if they will include information on the small scale i intend to use it for.

thank you more than you can imagine, mark grossman

[oasis]

Mark,

The depths cited are for a big filter. I've made one scaled down to a 55 gallon drum, which should be fine for a single families drinking water.

I have drawings of this thing but have not published them. You could try to prod us to do the work of making it a downloadable item.

A few hints: use a plastic drum. You want a float valve on the inlet, and a drain in the bottom where you can remove any fines that settle to the bottom of the gravel layer. Also, ideally the outlet water would be collected in a reservoir so you are not so limited as to flow rate when you want to fill up. This could be another 55 gallon next to the first, connected at the bottom, with an outlet several inches up from any sediment, and a drain (could be one pass through with the removable drain/ outlet extension pictured in water storage.) As this second drum fills, the rate of filtration will automatically slow, as the head lessens, ultimately stopping when the level common to the two drums reaches the shut off level of the float valve.


Our water quality testing packet explains how you can do your own coliform tests, which would empirically confirm if your filter was working or not.

Good luck!

Art

[markgrossman]

hi art, ok, so i got around to making my own figures for a 50 gallon drum and wanted to compare notes.

i got the levels in this order, from top to bottom, and size

15 cm air space with floater valve
15 cm water
mosquito type screen
30 cm fine sand
10 cm rough sand
5 cm small gravel
5 cm big gravel

this equals 80 cm of space needed and a 50 gallon drum here is about 88 cm high on the outside so it leaves some room for different size drums