Using Graywater
and Stormwater
to Enhance Local Water Supplies

AN ASSESSMENT OF RISKS, COSTS, AND BENEFITS

Committee on the Beneficial Use of Graywater and Stormwater:
An Assessment of Risks, Costs, and Benefits

Water Science and Technology Board

Division on Earth and Life Studies

THE NATIONAL ACADEMIES PRESS500 Fifth Street, NWWashington, DC 20001

This activity was supported by the City of Madison, Wisconsin; Grant No. EP-C-09-003, TO #23 and EP-C-14-005, TO #9 from the U.S. Environmental Protection Agency; the Los Angeles Department of Water and Power; this material is based on work supported by the National Science Foundation under Grant No. CBET-1321776; the National Water Research Institute; the Water Environment Research Foundation; the Water Research Foundation Agreement No. 04521; the WateReuse Research Foundation; and with additional support from the National Academy of Sciences Arthur L. Day Fund, the National Academy of Sciences W.K. Kellogg Foundation Fund, and the National Academy of Sciences George and Cynthia Mitchell Endowment for Sustainability Science. Any opinions, findings, conclusions, or recommendations expressed in this publication do not necessarily reflect the views of any organization or agency that provided support for the project.

International Standard Book Number-13: 978-0-309-38835-1
International Standard Book Number-10: 0-309-38835-X
Digital Object Identifier: 10.17226/21866

Cover credit (clockwise from top left): Images courtesy of Water Replenishment District of Southern California; Innovative Water Solutions, LLC, Austin, Texas; and Mother Earth News.

The National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, nongovernmental institution to advise the nation on issues related to science and technology. Members are elected by their peers for outstanding contributions to research. Dr. Ralph J. Cicerone is president.

The National Academy of Engineering was established in 1964 under the charter of the National Academy of Sciences to bring the practices of engineering to advising the nation. Members are elected by their peers for extraordinary contributions to engineering. Dr. C. D. Mote, Jr., is president.

The National Academy of Medicine (formerly the Institute of Medicine) was established in 1970 under the charter of the National Academy of Sciences to advise the nation on medical and health issues. Members are elected by their peers for distinguished contributions to medicine and health. Dr. Victor J. Dzau is president.

The three Academies work together as the National Academies of Sciences, Engineering, and Medicine to provide independent, objective analysis and advice to the nation and conduct other activities to solve complex problems and inform public policy decisions. The Academies also encourage education and research, recognize outstanding contributions to knowledge, and increase public understanding in matters of science, engineering, and medicine.

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COMMITTEE ON THE BENEFICIAL USE OF GRAYWATER AND STORMWATER: AN ASSESSMENT OF RISKS, COSTS, AND BENEFITS

RICHARD G. LUTHY, Chair, Stanford University, California

RICHARD W. ATWATER, Southern California Water Committee, Studio City, California

GLEN T. DAIGGER, University of Michigan, Ann Arbor

JÖRG DREWES, Technische Universität München, Garching, Germany

BENJAMIN H. GRUMBLES, Maryland Department of the Environment, Baltimore

ARPAD HORVATH, University of California, Berkeley

ROBERT E. PITT, University of Alabama, Tuscaloosa

MARCUS M. QUIGLEY, OptiRTC, Boston, Massachusetts

ROBERT S. RAUCHER, Stratus Consulting/Abt Associates, Boulder, Colorado

SYBIL SHARVELLE, Colorado State University, Fort Collins

CLAIRE WELTY, University of Maryland Baltimore County

MARYLYNN V. YATES, University of California, Riverside

Academies Staff

STEPHANIE E. JOHNSON, Study Director, Water Science and Technology Board

MICHAEL J. STOEVER, Research Associate, Water Science and Technology Board

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Preface

Much of the United States faces chronic or episodic water shortages. It is the topic of daily news in the West, where a historic 4-year drought has caused California to restrict the delivery of water to cities and farms. At the same time, the Midwest and Northeast have received drenching rains and heavier than normal snow. Against this backdrop—of not enough water or too much water—the National Academies of Sciences, Engineering, and Medicine’s Water Science and Technology Board initiated a study on the beneficial use of stormwater and graywater. Graywater is a year-round source of water for nonpotable use, and use of urban stormwater can augment local water supplies, reduce demand for imported water, and lessen impacts from discharge.

As detailed in this report, increased attention to the use of stormwater and graywater has been driven by factors forcing change in the design and management of urban water supplies and infrastructure. Among the drivers are water scarcity in regions of the country facing water shortages and the impacts of climate change and population growth that exacerbate these shortages. In these places stormwater and graywater use may diversify the water supply portfolio, thereby achieving greater resiliency in the face of uncertain water deliveries. Furthermore, in many parts of the country—from the humid midcontinent to coastal cities—pollution control and discharges to impaired water bodies are driving changes in the ways that stormwater is managed, and stormwater capture and use can reduce pollution from urban runoff, including combined sewer overflows.

Stormwater and graywater use exemplify a growing trend of embracing sustainable urban water management and green design practices. The concept of a re-imagined urban water infrastructure—variously termed low-impact design, blue-green city, or water sensitive city—embraces sustainable practices in which metropolitan regions could serve as water supply catchments, provide ecosystem services, and prioritize livability, sustainability, and resilience. However, realizing this vision raises questions on exactly how graywater and urban stormwater should be captured, stored, and used. Because of the absence of ample documentation of costs, performance, and risks, many utilities are hesitant to integrate the practices into their long-term water resource plans beyond the simplest applications. Potential public health risks from microbial or chemical contamination associated with graywater or stormwater use raise concerns about safety, regulation, and management. To better address these challenges, the Academies formed a committee to study the risks, costs, and benefits of stormwater and graywater use to augment and conserve existing water supplies. Although there are challenges in advancing ever-more use of graywater and urban stormwater, this report documents the committee’s finding that graywater and urban stormwater have substantial potential to contribute to local water supply needs while providing other benefits such as stormwater pollution reduction, water supply diversification, and increased local control of water supplies. Graywater and stormwater use could be an important part of a broader effort to reimagine urban water infrastructure to efficiently use water, energy, and financial resources while enhancing water supply reliability and resiliency and the livability of cities.

This study was supported with funding from the Environmental Protection Agency Office of Water and Office of Research and Development; National Science Foundation; Water Research Foundation; Water Environment Research Foundation; Los Angeles Department of Water and Power; WateReuse; City of Madison, Wisconsin; National Water Research Institute; and the National Academies’ President’s fund. We appreciate the sponsor liaisons, including Robert Bastian, Robert Goo, Christopher Kloss, John Whitler, and Andy Niknafs, for help with information gathering in support of the study and the many presenters to the committee for the helpful insights provided. The committee also appreciates the research assistance from Amy Streitwieser, Adam Schempp, Will Derwin, Jonathan Bradshaw, and Thomas Hendrickson.

The committee had the excellent fortune to be assisted by a dedicated and talented Academies staff, including Stephanie Johnson and Michael Stoever. I speak for the entire committee in expressing our profound respect and appreciation to Stephanie Johnson for her tireless effort and clear thinking. This report would not have been possible without her exceptional support and good humor.

I very much enjoyed working with the Academies’ staff and the committee members. I am sure each of us learned more than we contributed, and we offer this report in hopes that it will advance our nation on a path toward more sustainable urban water futures.

Richard Luthy, Chair

Committee on the Beneficial Use of Graywater and

Stormwater: An Assessment of Risks, Costs, and Benefits

Acknowledgment of Reviewers

This report has been reviewed in draft form by persons chosen for their diverse perspectives and technical expertise. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making the published report as sound as possible and to ensure that it meets institutional standards of objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their review of this report:

Nicholas Ashbolt, University of Alberta

Michael Barrett, University of Texas

Peter Dillon, International Association of Hydrogeologists Commission on Management of Aquifer Recharge

Jerome B. Gilbert, Consulting Engineer

Peter Gleick, Pacific Institute for Studies in Development, Environment, and Security

Eberhard Morgenroth, Eawag

Sheila Olmstead, University of Texas

Kevin Price, Middle East Desalination Research Center

Karl Rockne, University of Illinois at Chicago

Larry A. Roesner, Colorado State University

Bahman Sheik, Independent Water Resources and Reuse Specialist

Eric W. Strecker, Geosyntec, Inc.

Rhodes Trussell, Trussell Technologies, Inc.

Wendy E. Wagner, University of Texas School of Law

Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations, nor did they see the final draft of the report before its release. The review of this report was overseen by Kenneth W. Potter, University of Wisconsin, and Michael Kavanaugh, Geosyntec, Inc. They were responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.

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Contents