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Summary: All about all aspects of grey water systems. Why to use them, how to choose, build and use them, regulations, studies, and examples. Includes grey water irrigation, grey water treatment, grey water filters, and indoor grey water reuse.
Grey water informationGrey water booksSystem examplesGrey water regulation |
What is grey water?Any water 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.
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:
Is grey water legal?In practice, greywater 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 or New Mexico. For details see our Grey water policy center and Builder's Grey Water Guide (book).
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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.
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.
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.
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 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.
Grey water application in excess of plant needs recharges groundwater.
Grey water enables a landscape to flourish where water may not otherwise be available to support much plant growth.
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.
Grey water use yields the satisfaction of taking responsibility for the wise husbandry of an important resource.
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