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New Water Resource: Graywater

August 25th, 2010

According to the US EPA, an average American family of four uses about 400 gallons of water per day to meet indoor and outdoor needs. More than half of the water used indoors is suitable for reuse in non-potable applications like irrigation or toilet flushing. This reusable water, also known as “graywater,” is effluent that has not mixed with human excrement or organics. Water from the lavatory, laundry machine, and shower or bath is considered graywater.

Why use clean, potable water to irrigate the lawn or flush a toilet when graywater will work just as well? There are some sanitary concerns associated with graywater, but with sound research and development graywater reuse has become a safe way to reduce demand on municipal supplies and often fragile water resources.  The San Francisco Public Utilities Commission will become the first building in San Francisco to permit the treatment and reuse of graywater for toilet flushing. A recent article by the Christian Science Monitor discusses this next battle ground as we face dwindling water resources.

A rendering by KMD Architects of the proposed SF PUC building

John Leys, lead reviewer
Bry Sarté, peer review
Nick Lee, research






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