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Grey Water Central

The web's information central on all aspects of grey water systems
from the leading innovators and producers of greywater information


Why to use grey water, how to choose, build and use grey water reuse systems, regulations, studies, science and examples. Grey water irrigation, treatment, filtration, low tech DIY systems, high tech indoor grey water reuse...

For homeowners, do-it-yourselfers, regulators, inspectors, elected officials, building departments, health departments, builders, and activists.

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Why you can trust this information

The quality and credibility of our information is the key to our livelihood; 99% of our income is from information. We have developed numerous greywater reuse innovations. All have been published unpatented into the public domain. We don't have as much stake in any particular system as we have in being a trustworthy information source for all ecological design. When no greywater system is appropriate, we gain credibility by saying so. Likewise if a manufactured system is more suited than a DIY system we developed. When a better way of reusing greywater is found, we just update our information--we don't have a warehouse full of obsolete systems to be stuck with. (Our main greywater book is currently in its 19th revision!) <More about Why you can trust this info>

You'll find older versions of this content replicated all over the web; this is the source. We appreciate your links, likes, and direct book purchases; they support our public service research, development, and free content.

We hope this information helps you manage your resources wisely--

--The Oasis Team



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Beautiful permaculture garden irrigated with branched drain gray water system
Greywater irrigated garden in state of CA study

What is grey water?

Any washwater that has been used in the home, except water from toilets, is called grey water. Dish, shower, sink, and laundry water comprise 50-80% of residential "waste" water. This may be reused for other purposes, especially landscape irrigation.

(This is the definition common in Europe and Australia. Some jurisdictions in the US exclude kitchen sink water and diaper wash water from their definition of grey water. These are most accurately defined as "dark grey water")


Why use grey water?

It's a waste to irrigate with great quantities of drinking water when plants thrive on used water containing small bits of compost. Unlike a lot of ecological stopgap measures, grey water reuse is a part of the fundamental solution to many ecological problems and will probably remain essentially unchanged in the distant future. The benefits of grey water recycling include:

  • Lower fresh water use
  • Less strain on failing septic tank or treatment plant
  • Better treatment (topsoil is many times more effective than subsoil or treatment plant)
  • Less energy and chemical use
  • Groundwater recharge
  • Plant growth
  • Reclamation of otherwise wasted nutrients
  • Increased awareness of and sensitivity to natural cycles

Fruit harvested from agro-forestry system.

Healthy fruit from sanitary irrigation of edible landscape


Why does grey water matter?

Viewed narrowly, grey water systems don’t look that important. A low flow showerhead can save water with less effort. A septic system can treat grey water almost as well.
But when you look at the whole picture—how everything connects—the keystone importance of grey water is revealed.

  • Ecological systems design is about context, and integration between systems. The entirety of integrated, ecological design can be reduced to one sentence: do what's appropriate for the context.
  • Ecological systems—rainwater harvesting, runoff management, passive solar, composting toilets, edible landscaping—all of these are more context sensitive than their counterparts in conventional practice; that's most of what makes them more ecological.
  • Grey water systems are more context sensitive than any other man-made ecological system, and more connected to more other systems.
  • Get the grey water just right, and you’ve got the whole package right—and that matters.

Many people and organizations instinctively recognize that grey water is the ideal test case for the transition to a new way of regulating and building that is appropriate to a post-peak resource, mature civilization.

The US Green Building Council, the City of Santa Barbara, CA, Oregon ReCode, and SLO Green Build are among those organizations which independently chose grey water standards as the technology with which to launch their programs of regulatory reform.


Is grey water reuse safe?

Yes. There are eight million grey water systems in the US with 22 million users. In 60 years, there have been one billion system user-years of exposure, yet there has not been one documented case of grey water transmitted illness.

(In contrast, 400 Americans get hit by lightning each year. More details, calculations and references).


Is grey water legal?

In practice, grey water legality is virtually never an issue for residential retrofit systems—everyone just bootlegs them. However, grey water legality is almost always an issue for permitted new construction and remodeling, unless you're in a visionary state such as Arizona, New Mexico, Texas (and soon, NV, MT, OR, and CA). For details see our Grey water policy center and  Builder's Grey Water Guide (book).




The benefits of grey water recycling (in detail)

* Lower fresh water use

Grey water can replace fresh water in many instances, saving money and increasing the effective water supply in regions where irrigation is needed. Residential water use is almost evenly split between indoor and outdoor. All except toilet water could be recycled outdoors, achieving the same result with significantly less water diverted from nature.

* Less strain on septic tank or treatment plant

Grey water use greatly extends the useful life and capacity of septic systems. For municipal treatment systems, decreased wastewater flow means higher treatment effectiveness and lower costs.

* Highly effective purification

Grey water is purified to a spectacularly high degree in the upper, most biologically active region of the soil. This protects the quality of natural surface and ground waters.

* Site unsuitable for a septic tank

For sites with slow soil percolation or other problems, a grey water system can be a partial or complete substitute for a very costly, over-engineered system.

* Less energy and chemical use

Less energy and chemicals are used due to the reduced amount of both freshwater and wastewater that needs pumping and treatment. For those providing their own water or electricity, the advantage of a reduced burden on the infrastructure is felt directly. Also, treating your wastewater in the soil under your own fruit trees definitely encourages you to dump fewer toxic chemicals down the drain.

* Groundwater recharge

Grey water application in excess of plant needs recharges groundwater.

* Plant growth

Grey water enables a landscape to flourish where water may not otherwise be available to support much plant growth.

* Reclamation of otherwise wasted nutrients

Loss of nutrients through wastewater disposal in rivers or oceans is a subtle, but highly significant form of erosion. Reclaiming nutrients in grey water helps to maintain the fertility of the land.

* Increased awareness of and sensitivity to natural cycles

Grey water use yields the satisfaction of taking responsibility for the wise husbandry of an important resource.



Further reading and watching from the bookstore

Create an Oasis with Grey Water (book)

Laundry to Landscape (DVD)

Builder's Grey Water Guide (book)

New Greywater Book and Video Set: The New Create an Oasis, Builder's Greywater Guide, Principles of Ecological Design, Laundry to Landscape instructional DVD $51.80 ($13 savings)

Excerpt from our instructional Laundry to Landscape (DVD):
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