A report by the Water Science and Technology Board of the National Academies of Sciences, Engineering and Medicine acknowledges that while technologies for graywater and stormwater capture and treatment for “fit-for-purpose” uses are mature, broader implementation of these technologies is stunted by the absence of risk-based guidelines. The recently released report, Using Graywater and Stormwater to Enhance Local Water Supplies: An Assessment of Risks, Costs, and Benefits, was developed by an ad-hoc committee tasked with addressing risks, costs and benefits of the beneficial uses of stormwater and graywater. The report addresses the following issues:
Assessing the quantity and suitability of stormwater capture and graywater reuse in the U.S. and how an increase in the beneficial use of this water would affect water demand and downstream uses including aquifer recharge and ecological flows;
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Treatment and storage technology currently available for stormwater and graywater capture and use;
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Human health and environmental risks and the state of regulatory frameworks to protect human health and the environment;
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Costs and benefits, including non-monetized costs and benefits;
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Legal and regulatory constraints on the implementation of using stormwater and graywater; and
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Research priorities.
The report acknowledges the constraints that water rights law places on the potential implementation of smaller-scale stormwater and graywater projects in the west. It also notes that larger stormwater and graywater use projects can take advantage of economies of scale, particularly on a neighborhood or regional level. Most research needs identified would help enhance decisionmaking for developing larger systems, such as developing treatment systems to meet fit-for-purpose water quality objectives and monitoring strategies for assuring compliance with water quality criteria.
The authors recommend additional examination of the health and environmental risks of using stormwater and graywater, noting that pathogens represent the most significant risks.
A lack of authoritative risk-based guidelines for stormwater and graywater design and application in the U.S. is impeding their expanded use, they say.