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Greywater Reuse Can Save Thousands of Gallons of Drinking Water

Photo: Courtesy of Hannah Xu on Unsplash

Sharon Steiner

NSF International, Wastewater Treatment Unit Program

New data shows widespread drought conditions emerging in California and the American west as bad as or worse than prehistoric events recorded by 1,200 years of tree ring data. The Earth Institute at Columbia University characterizes it as a rare megadrought.

The U.S. Drought Monitor, as of May 5, 2020, showed 39 percent of California is experiencing a moderate to severe drought with common or developing water shortages and imposed and voluntary restrictions on water usage. Another 15 percent of the state is currently experiencing abnormally dry conditions.

The San Francisco area has received just 50 percent of its normal rainfall so far this year, and the northwest portion of California is in severe drought conditions. Droughts are a recurring part of the state’s history, and this new extreme period of water shortage follows what was already the longest drought in the state’s history, from 2011 to 2019.

The commitment to conserve our precious drinking water that is essential to life is more critical than ever.

Reusing greywater

One way we can do this is by reusing greywater, treated water from showers and laundry, to flush toilets or water our lawns.

NSF/ANSI 350 is a standard that sets minimum requirements for greywater reuse treatment systems using water-saving technology for these nonpotable functions.

A typical certified greywater reuse system can save up to 1,500 gallons of fresh water daily in each home where it is in use and can be scaled up for larger commercial reuse. These systems also earn credits toward LEED certification.

Testing to the standard is rigorous and is conducted over a 26-week period. Certification to NSF/ANSI 350 assures consumers and public health regulators that the treated greywater reduces particulates, risk of E. Coli, and carbonaceous biochemical oxygen demand (CBOD5) to the required scientific effluent levels.

Setting standards

NSF International, a global public health organization, facilitated development of the standard using the American National Standards Institute process, which ensures balanced input from industry representatives, public health/regulatory officials, and users/consumer representatives.

As prolonged drought conditions persist in California and throughout America’s west, reuse of greywater treated through a residential or commercial certified system helps conserve one of our most vital resources: fresh drinking water. 

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