Drinking Water Distribution Systems: Assessing and Reducing Risks

404 Pages·2006·5.94 MB·English

by  National Research Council

DRINKING WATER DISTRIBUTION SYSTEMS
A S S E S S I N G A N D R E D U C I N G R I S K S

Committee on Public Water Supply Distribution Systems:
Assessing and Reducing Risks

Water Science and Technology Board

Division on Earth and Life Studies

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NOTICE: The project that is the subject of this report was approved by the
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from the councils of the National Academy of Sciences, the National Academy
of Engineering, and the Institute of Medicine. The members of the committee
responsible for the report were chosen for their special competences and with
regard for appropriate balance.

Support for this project was provided by EPA Contract No. 68-C-03-081. Any
opinions, findings, conclusions, or recommendations expressed in this
publication are those of the author(s) and do not necessarily reflect the views of
the organizations or agencies that provided support for the project.

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vi
COMMITTEE ON PUBLIC WATER SUPPLY DISTRIBUTION SYSTEMS:
ASSESSING AND REDUCING RISKS

VERNON L. SNOEYINK, Chair, University of Illinois, Urbana-Champaign
CHARLES N. HAAS, Vice-Chair, Drexel University, Philadelphia,
Pennsylvania
PAUL F. BOULOS, MWH Soft, Broomfield, Colorado
GARY A. BURLINGAME, Philadelphia Water Department, Philadelphia,
Pennsylvania
ANNE K. CAMPER, Montana State University, Bozeman
ROBERT N. CLARK, Environmental Engineering and Public Health
Consultant, Cincinnati, Ohio
MARC A. EDWARDS, Virginia Polytechnic and State University, Blacksburg
MARK W. LECHEVALLIER, American Water, Voorhees, New Jersey
L. D. MCMULLEN, Des Moines Water Works, Des Moines, Iowa
CHRISTINE L. MOE, Emory University, Atlanta, Georgia
EVA C. NIEMINSKI, Utah Department of Environmental Quality, Salt Lake
City
CHARLOTTE D. SMITH, Charlotte Smith and Associates, Inc., Orinda,
California
DAVID P. SPATH, California Department of Health Services (Retired),
Sacramento
RICHARD L. VALENTINE, University of Iowa, Iowa City

National Research Council Staff

LAURA J. EHLERS, Study Director
ELLEN A. DE GUZMAN, Research Associate

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WATER SCIENCE AND TECHNOLOGY BOARD

R. RHODES TRUSSELL, Chair, Trussell Technologies, Inc., Pasadena,
California
MARY JO BAEDECKER, U.S. Geological Survey (Retired), Vienna, Virginia
JOAN G. EHRENFELD, Rutgers University, New Brunswick, New Jersey
DARA ENTEKHABI, Massachusetts Institute of Technology, Cambridge
GERALD E. GALLOWAY, Titan Corporation, Reston, Virginia
SIMON GONZALES, National Autonomous University of Mexico, Mexico
CHARLES N. HAAS, Drexel University, Philadelphia, Pennsylvania
KIMBERLY L. JONES, Howard University, Washington, DC
KAI N. LEE, Williams College, Williamstown, Massachusetts
JAMES K. MITCHELL, Virginia Polytechnic Institute and State University,
Blacksburg
CHRISTINE L. MOE, Emory University, Atlanta, Georgia
ROBERT PERCIASEPE, National Audubon Society, New York, New York
LEONARD SHABMAN, Resources for the Future, Washington, DC
HAME M. WATT, Independent Consultant, Washington, DC
CLAIRE WELTY, University of Maryland, Baltimore County
JAMES L. WESCOAT, JR., University of Illinois, Urbana-Champaign
GARRET P. WESTERHOFF, Malcolm Pirnie, Inc., White Plains, New York

Staff

STEPHEN D. PARKER, Director
LAUREN E. ALEXANDER, Senior Staff Officer
LAURA J. EHLERS, Senior Staff Officer
JEFFREY W. JACOBS, Senior Staff Officer
STEPHANIE E. JOHNSON, Senior Staff Officer
WILLIAM S. LOGAN, Senior Staff Officer
M. JEANNE AQUILINO, Financial and Administrative Associate
ANITA A. HALL, Senior Program Associate
ELLEN A. DE GUZMAN, Research Associate
JULIE VANO, Research Associate
DOROTHY K. WEIR, Research Associate
MICHAEL J. STOEVER, Project Assistant

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Preface

The distribution system is a critical component of every drinking water
utility. Its primary function is to provide the required water quantity and quality
at a suitable pressure, and failure to do so is a serious system deficiency. Water
quality may degrade during distribution because of the way water is treated or
not treated before it is distributed, chemical and biological reactions that take
place in the water during distribution, reactions between the water and
distribution system materials, and contamination from external sources that
occurs because of main breaks, leaks coupled with hydraulic transients, and
improperly maintained storage facilities, among other things. Furthermore,
special problems are posed by the utility’s need to maintain suitable water
quality at the consumers tap, and the quality changes that occur in consumers’
plumbing, which is not owned or controlled by the utility.
The primary driving force for managing and regulating distribution systems
is protecting the health of the consumer, which becomes more difficult as our
nation’s distribution systems age and become more vulnerable to main breaks
and leaks. Certainly factors that cause water of poor aesthetic quality to be
delivered to the tap, or that increase the cost of delivering water, are also
important. Possibly because they are underground and out of sight, it is easy to
delay investments in distribution systems when budgets are considered. Rather
than wait for further deterioration, however, there is an urgent need for new
science that will enable cost-effective treatment for distribution, and design,
construction, and management of the distribution system for protection of public
health and minimization of water quality degradation.
This report was undertaken at the request of the U.S. Environmental
Protection Agency (EPA) and was prepared by the Water Science and
Technology Board (WSTB) of the National Research Council (NRC). The
committee formed by the WSTB conducted a study of water quality issues
associated with public water supply distribution systems and their potential risks
to consumers. Although the report focused on public systems that serve at least
25 people, much that is said in the report is also applicable to private, individual
distribution systems. The study considered regulations and non-regulatory
approaches to controlling quality; the health effects of distribution system
contamination; physical, hydraulic, and water quality integrity; and premise
plumbing issues. Important events that constitute health risks, such as cross
connections and backflow, pressure transients, nitrification and microbial
growth, permeation and leaching, repair and replacement of water mains, aging
infrastructure, corrosion control, and contamination in premise plumbing, were
examined. The activities of the Committee included the following tasks:

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viii PREFACE

1—As background and based on available information, identification of
trends relevant to the deterioration of drinking water in water supply distribution
systems.

2—Identification and prioritization of issues of greatest concern for
distribution systems based on review of published material.

3—Focusing on the highest priority issues as revealed by task #2, (a)
evaluation of different approaches to characterization of public health risks
posed by water-quality deteriorating events or conditions that may occur in
public water supply distribution systems; and (b) identification and evaluation
of the effectiveness of relevant existing codes and regulations and identification
of general actions, strategies, performance measures, and policies that could be
considered by water utilities and other stakeholders to reduce the risks posed by
water-quality deteriorating events or conditions. Case studies were identified
and recommendations were presented in their context.

4—Identification of advances in detection, monitoring and modeling,
analytical methods, information needs and technologies, research and
development opportunities, and communication strategies that will enable the
water supply industry and other stakeholders to further reduce risks associated
with public water supply distribution systems.

The Committee prepared an interim report entitled “Public Water Supply
Distribution Systems: Assessing and Reducing Risks, First Report” in March
2005 that dealt with the first two tasks listed above; the interim report has been
incorporated into this report in order to make this report a complete compilation
of Committee’s activities. The third and fourth tasks constitute the subject
matter of the present report; an explanation of where individual issues are
discussed in the report can be found at the end of Chapter 1.
The EPA is in the process of considering changes to the Total Coliform
Rule (TCR), which is one of the existing rules governing water quality in
distributions systems. This report does not include a comprehensive evaluation
of the science behind the TCR, a critique of that science, or specific suggestions
on how to change the Rule. However, the Committee believes that this report
should be considered when developing changes to the Rule, in order to
determine whether the revised Rule could better encompass distribution system
integrity.
When preparing the report the committee made a series of assumptions that
affected the outcome of the report. First, it was assumed that both treated and
distributed water has to meet U.S. water quality standards. Second, water
distribution will almost certainly be accomplished with the existing
infrastructure in which the nation has invested billions of dollars and which is
continuously being expanded. Thus, the report focuses on how to best use
PREFACE ix

traditionally designed distribution systems in which potable water is distributed
for all uses. These assumptions led the Committee to devote only a small
section of the report to non-traditional distribution system design (such as dual
distribution systems), investigation of which was not in the Committee’s charge.
The Committee believes that alternative methods of distributing water,
including dual distribution systems, point-of-use and point-of-entry treatment
systems, and community-based treatment systems need more research and
evaluation to determine their effectiveness and applicability, both in the United
States and elsewhere in the world. The Committee did not consider lead and
copper corrosion because this subject is part of the Lead and Copper Rule and
for this reason was intentionally excluded from the committee’s charge by the
study sponsor. Corrosion in distribution systems, in general, has very important
impacts on water quality in distribution systems, and the committee believes that
state-of-the-art internal and external corrosion control procedures should be
made available to the industry, perhaps in the form of a manual of practice.
Finally, at the request of EPA, the committee did not consider issues
surrounding the security of the nation’s distribution systems, including potential
threats and monitoring needed for security purposes.
In developing this report, the Committee benefited greatly from the advice
and input of EPA representatives, including Ephraim King, Yu-Ting Guilaran,
Elin Betanzo, and Kenneth Rotert and from presentations by Russ Chaney,
IAPMO; Barry Fields, CDC; Johnnie Johannesen, Matt Velardes, and Chris
Kinner, Irvine Ranch Water District; Laura Jacobsen, Las Vegas Valley Water
District; Dan Kroll, HACH HST; Kathy Martel, Economic and Engineering
Services; Pankaj Parehk, LA Department of Water and Power; Paul Schwartz,
USC Foundation for Cross-Connection Control and Hydraulic Research; and
Walter J. Weber, Jr., University of Michigan. We also thank all those who took
time to share with us their perspectives and wisdom about the various issues
affecting the water resources research enterprise.
The Committee was ably served by the staff of the Water Science and
Technology Board and its director, Stephen Parker. Study director Laura Ehlers
kept the Committee on task and on time, provided her own valuable insights
which have improved the report immeasurably, and did a superb job of
organizing and editing the report. Ellen de Guzman provided the Committee
with all manner of support in a timely and cheerful way. This report would not
have been possible without the help of these people.
This report has been reviewed in draft form by individuals chosen for their
diverse perspectives and technical expertise, in accordance with procedures
approved by the NRC’s Report Review Committee. The purpose of this
independent review is to provide candid and critical comments that will assist
the institution in making its published report as sound as possible and to ensure
that the report meets institutional standards for objectivity, evidence, and
responsiveness to the study charge. The review comments and draft manuscript