New Report on Graywater and Stormwater

Water scarcity, population growth, and climate change have driven increased interest in the use of stormwater and graywater as a means to diversify water supply portfolios. WRF contributed funding to a recently-published report on graywater and stormwater, Using Graywater and Stormwater to Enhance Local Water Supplies: An Assessment of Risks, Costs, and Benefits. This project convened a committee of knowledge experts to conduct a study of on-site water reuse of stormwater and graywater. The study also investigated safety and regulations related to treatment and storage of stormwater capture and graywater reuse for various end uses.

The project deliverables were published by the National Academies Press, and include a four-page “Report in Brief” and a full report. The Report in Brief is posted on the WRF website on the #4521 project page. The full report can be downloaded for free on the National Academies Press website.

On a small scale, some households and businesses across the United States capture graywater and stormwater for toilet flushing and outdoor irrigation. On a larger neighborhood or regional scale, some municipalities capture stormwater to recharge groundwater. Graywater and stormwater can supplement water supplies, reduce pollution, and ease the burden on wastewater facilities. Despite these benefits, utilities need more concrete information about capturing, storing, and using graywater.

In order to evaluate the potential water savings from graywater and stormwater use, the project team carried out an original scenario analysis on six U.S. locations, assuming medium-density residential development. The research team found that household-scale stormwater capture in eastern/central U.S. cities has the highest potential for water savings (24–28%). It was estimated that household-scale water capture in the two western locations, Los Angeles and Seattle, would yield less water savings (5 and 15%, respectively).

The project’s investigation of microbial and chemical contamination found that disinfection is necessary for many uses of graywater, including toilet flushing, spray irrigation, and food crop irrigation.

In addition to WRF, the following organizations also contributed funding to this project: The National Academies of Sciences, Engineering, and Medicine; the U.S. Environmental Protection Agency; National Science Foundation; Water Environment Research Foundation; Los Angeles Department of Water and Power; WateReuse Foundation; City of Madison, Wisconsin; National Water Research Institute; and The National Academies’ President’s Fund.