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The web's information central on all aspects of graywater systems.


Summary: Why to use graywater , how to choose, build and use graywater reuse systems, regulations, studies, science and examples. Includes graywater irrigation, graywater treatment, graywater filters, high tech indoor graywater reuse and graywater management in developing countries.

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

Oasis Design is a—quite possibly the—preeminent source of trustworthy source of greywater information since 1989.

Oasis Design has walked central, neutral ground between warring factions during sweeping
changes in the emergent greywater industry. Our information and consulting clients entrust us with their darkest greywater secrets, system manufacturers keep us abreast of their offerings, academics appreciate our research. As we have become the world’s greywater “information central,” regulators increasingly seek us out for help directing policy and writing standards.

We publish the most popular books on greywater; have developed numerous key greywater innovations and published them free and unpatented into the public domain, includingBranched Drain Graywater Systemsand theLaundry to Landscapesystem; developed the first plant and soil biocompatible laundry detergent; and helped develop better grey water policies and scientific understanding.

Since we don't sell any system, it's easy for us to be totally neutral about hardware. (We developed the world's first plant and soil biocompatible laundry detergent, but we sold that business in 1996.) Most contradictory information you'll find is from manufacturers with a stake in a particular system.

We give away most of our information. Approximately 30% of our livelihood is from sales of the Create an Oasis with Greywater book. Quality and credibility of our information is the key to our livelihood

You'll find older versions of this content replicated all over the web; this is the source. We appreciate the links and book purchases which 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 graywater ?

Any washwater that has been used in the home, except water from toilets, is called graywater . 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 graywater . These are most accurately defined as "dark graywater ")


Why use graywater ?

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, graywater 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 graywater 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 graywater matter?

Viewed narrowly, graywater systems don’t look that important. A low flow showerhead can save water with less effort. A septic system can treat graywater almost as well.
But when you look at the whole picture—how everything connects—the keystone importance of graywater 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.
  • Graywater systems are more context sensitive than any other man-made ecological system, and more connected to more other systems.
  • Get the graywater just right, and you’ve got the whole package right—and that matters.

Many people and organizations instinctively recognize that graywater 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 graywater standards as the technology with which to launch their programs of regulatory reform.


Is graywater reuse safe?

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

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

Is graywater legal?

In practice, graywater legality is virtually never an issue for residential retrofit systems—everyone just bootlegs them. However, graywater 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 Graywater Guide (book).



The benefits of graywater recycling (in detail)

* Lower fresh water use

Graywater 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

Graywater 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

Graywater 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 graywater 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

Graywater application in excess of plant needs recharges groundwater.

* Plant growth

Graywater 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 graywater helps to maintain the fertility of the land.

* Increased awareness of and sensitivity to natural cycles

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


Further reading and watching from the bookstore

The New Create an Oasis with Graywater (book)

Laundry to Landscape (DVD)

Builder's Graywater Guide (book)

New Greywater Book and Video Set: Create an Oasis, Builder's Greywater Guide, Principles of Ecological Design, Laundry to Landscape instructional DVD $49.80 ($13 savings)

Excerpt from our instructional Laundry to Landscape (DVD):


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