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Report shows benefits, risks of stormwater and graywater

Report shows benefits, risks of stormwater and graywater
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There’s a lot of potential benefit to capturing graywater and stormwater to supplement traditional water supplies, but it doesn’t make sense for everyone, and there are plenty of legal, regulatory and climate-related hurdles in doing so, says Colorado State University’s Sybil Sharvelle.

Sybil Sharvelle, Associate Professor of Civil and Environmental Engineering, Colorado State University, September 10, 2015

Sybil Sharvelle

Sharvelle, associate professor of civil and environmental engineering and head of CSU’s Urban Water Center, served on a 12-member national committee charged with addressing the benefits and challenges of stormwater and graywater as supplemental water sources, as the nation faces widespread water shortages and droughts. The National Academies report, released publicly Dec. 16, was two years in the making and provides information on the costs, benefits, risks and regulations associated with capturing these alternative water sources.

According to the report, stormwater is “water from rainfall or snow that can be measured downstream in a pipe, culvert or stream shortly after the precipitation event.” Graywater is “untreated wastewater that does not include water from the toilet or kitchen, and may include water from bathroom sinks, showers, bathtubs, clothes washers and laundry sinks.”

The report recommends best practices and treatment systems for the use of water from these sources; for example, in many locations with heavy rainfall, it’s possible to store excess water in aquifers for use during dry seasons. In some cases, stormwater captured at neighborhood and larger scales can substantially contribute to urban water supplies.

Graywater is best for non-potable uses like toilet flushing and subsurface irrigation. It has potential to help arid places like Los Angeles achieve substantial savings, and it serves as a year-round, reliable water source, according to the report. Larger irrigation systems and indoor reuse systems would require complex plumbing and treatment retrofits that are typically most appropriate for new, multi-residential buildings or neighborhoods for future urban planning.

The report cites the Eloy Detention Center in Arizona, which reuses graywater from showers and hand-washing to flush toilets. The facility has observed water savings of 20 gallons per day per inmate.

Sharvelle said the need for the report arose before the onset of widespread drought in the western United States.

“The use of these resources has been hindered by a lack of national guidance and ambiguous regulations for water quality targets,” Sharvelle said.

Sharvelle led an analysis of residential stormwater and graywater use in Los Angeles; Seattle; Newark; Madison, Wis.; Lincoln, Neb.; and Birmingham, Ala., and calculated potential savings for conservation irrigation and toilet flushing.

The bottom line is there’s no single best way to use these resources, because whether they’re successful or economically viable depend on a host of factors: legal and regulatory constraints, climate, and source water availability.

The report is online, and a webinar is planned for early 2016 to further detail the findings. The study was sponsored by the U.S Environmental Protection Agency, National Science Foundation and other agencies.

CSU’s Urban Water Center is part of the university’s One Water Solutions Institute, which seeks to connect CSU’s world-class research with real-world water challenges.

Anne Ju Manning

Anne Ju Manning