What is Grey Water?

What is Grey Water?

Water dropWhat is Greywater?

Greywater, defined by the California Health and Safety Code (Section 17922.12a) is “untreated wastewater that has not been contaminated by any toilet discharge, has not been affected by infectious, contaminated, or unhealthy bodily wastes, and does not present a threat from contamination by unhealthful processing, manufacturing, or operating wastes.” The Code also specifies what household sources can provide grey water: bathtubs, showers, bathroom washbasins, clothes washing machines, and laundry tubs. Any wastewater coming from kitchen sinks or dishwashers cannot be classified as greywater in California.
There are significant distinctions between greywater and toilet wastewater (called "blackwater"). These distinctions tell us how these wastewaters should be treated /managed and why, in the interests of public health and environmental protection, they should not be mixed together. For a copy of the handout click here.

Why use Greywater?

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, greywater 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 greywater 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