Greywater or Graywater is lightly used water from showers/baths, lavatory sinks and washing machines.
Whether from residential or commercial sources, greywater is a resource. It can be reused on-site for garden and lawn irrigation (see Laundry to Landscape & Simple Systems). Untreated it contains nutrients, such as nitrogen and phosphorus which benefit plant growth. Treated, it (See AQUALOOP) can be used for toilet flushing and laundry use (cold-water washing machine only unless you have a point of use water heater just for the laundry).
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
Reclamation of otherwise wasted nutrients
Increased awareness of and sensitivity to natural cycles
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 greywater 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 resuse 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 greywater transmitted illness.
(In contrast, 400 Americans get hit by lightning each year.