Summary: Why to use grey water, how to choose, build and use grey water reuse systems, regulations, studies, science and examples. Includes grey water irrigation, grey water treatment, grey water filters, high tech indoor grey water reuse and grey water recycling, grey water tanks, and grey water management in developing countries.
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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")
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:
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.
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.
Yes. There are eight million grey water 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 grey water transmitted illness.
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).
* 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.
Create an Oasis with Grey Water (book)
Laundry to Landscape (DVD)
Builder's Grey Water 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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