United States Science Advisory EPA-SAB-DWC-95-002
Environmental Protection Board March 1995
Agency Washington, DC 20460
<>EPA An SAB Report:
jUL i m Safe Drinking Water
ENVIRONMENTS
i PROTECTION
Future Trends and
Challenges LIBRARY
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
March 29,1995
EPA-SAB-DWC-95-002
OFFICE OF THE ADMINISTRATOR
SCIENCE ADVISORY BOARD
Honorable Carol M. Browner
Administrator
U.S. Environmental Protection Agency
401 M Street, SW
Washington, DC 20460
Subject: Safe Drinking Water: Future Trends and Challenges
Dear Ms. Browner:
As part of the Futures Project of the Science Advisory Board (SAB), the Drinking
Water Committee (DWC) has examined trends and issues likely to affect the future avail-
ability and quality of drinking water in the U.S. The primary goal of this exercise has been
to develop recommendations for strategies that would better enable the Agency and the
Nation to face the challenges posed by those trends in the next few decades.
This report is the result of the Committee's deliberations. In brief, the Committee
identified four broad trends that can be expected to seriously impact the future of drinking
water in the U.S.: a) increased population growth resulting in declining underground water
tables and increasingly contaminated water sources; b) increased public demand for cleaner
drinking water; c) a changing profile of chemical and microbial contaminants of concern in
drinking water; and, d) the resulting pressures to fundamentally change the manner in which
drinking water is produced. Based upon an analysis of these trends, the Committee agreed
upon five major recommendations, which are summarized later in this letter.
Although the U.S. is a relatively water-abundant country, and its population growth is
modest, current population trends are nonetheless sufficient to severely strain water re-
sources over time, particularly on a regional basis. One of the most serious problems in the
U.S. will be the continuing decline of groundwater tables, on which approximately 50% of
the U.S. population depends for drinking water. This decline is often related to agricultural
uses and practices, it is particularly serious in the western U.S., and is often accompanied
by increased contamination (e.g., by nitrates and toxic chemicals).
For surface waters, nonpoint sources of pollution will become the dominant threat.
Industrial point source contamination will continue to be an important concern for both
underground and surface waters, but the development of effective regulatory strategies to
control industrial discharges will continue to reduce the relative importance of this source
of pollution in the coming decades.
Increasing demands on renewable water resources will demand tough decisions
regarding the allocation of water resources. Competition between uses will increase, and
greater cooperation will be required between states and localities that comprise individual
watersheds. In order to address these conflicts, it will be necessary to modify the current
state water allocation systems so that they become more responsive to the trends in resource
availability and use, and particularly to facilitate increased conservation and reuse of water.
Also, the infrastructure of many U.S. water supply systems is old and in need of replace-
/Recydabk
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contains at toast 50% recycled fter
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ment, and many small and inefficient water supply systems will need to be consolidated
into larger systems.
Coupled with the increased pressures on water resources, there has been a growing
perception by the public that many drinking water supplies are contaminated repeatedly,
and tnis perception is likely to continue unabated in the next decades. Increased demands
for clean public water supplies also arise from the discovery of new information on health
effects (e.g., arsenic and lead) and from a declining tolerance on the part of the public to
"accept" any health risks. There are also growing expectations for the protection of virgin
natural resources that inevitably reduce the pool of resources available to supply drinking
water needs.
The chemical contaminants of primary concern in drinking water today, and in the
foreseeable future, arise from the chemical treatment of water whose goal is to remove the
risk of microbiological hazards. Many of these contaminants can be measured at Concentra-
tions that are so low that they exceed the ability of scientists to accurately estimate their
human health effects. At the same time, recent outbreaks of waterborne infectious disease
have focused attention on the shortcomings of current methods of water treatment, which
often do not adequately eliminate hazardous jnicroorganisms from treated waters. These
incidents also highlight the need to be extremely careful when modifying water treatment
systems in a manner that may give rise to new infectious disease risks.
The most difficult challenges to the production and delivery of safe drinking water in
the next decades, therefore, will be in the areas of evaluating and minimizing the competing
risks from chemical and microbiological contaminants that occur in water at very low
concentrations. Significant advances in toxicology and epidemiology will be needed to
overcome current gaps in scientific knowledge, including the development of better meth-
ods for extrapolation of animal data to humans and better dose-response models. In addi-
tion, it will be necessary to develop methods to compare microbial to chemical risks such
that decisions can be made that result in minimizing both types of risk.
The Committee examined the trends briefly described above, and their likely impacts
on the country's ability to provide safe drinking water in the future. As a result, the Com-
mittee agreed upon five major recommendations, as follows:
1. Improve the existing systems of management of renewable water
resources, including prevention of further water supply deteriora-
tion, better management of land-use and forestry practices, wetland
protection and extension, and implementation of water recycling and
conservation practices to improve efficiencies of water use.
2. Support the consolidation of small distribution systems to improve
the overall quality of water and provide the necessary revenue to
implement treatment technologies now available to the larger sys-
tems.
3. Support changes in treatment technologies to respond to the chang-
ing profiles of contaminants of concern.
4. Greatly accelerate research to spur advances in risk assessment
methodologies for both chemical and microbiological contaminants
of water to be able to more effectively guide large public invest-
ments for changes in drinking water treatment plants that may be
necessary.
5. Establish a surveillance or alert system to detect waterborne patho-
gens that may arise from changes and consolidation in water treat-
ment and distribution systems in the next decades.
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The attached report discusses these and other issues in more detail. We trust that the
identification of trends and challenges in the drinking water arena and the accompanying
recommendations, will be useful as you exercise your important responsibilities in the
future.
Sincerely,
jLw**^
Dr. Genevieve M. Matanoski, Chair
Executive Committee
Science Advisory Board
Dr. Raymond C. Loehr, Chair
Environmental Futures Committee
Science Advisory Board
Dr. Verne A. Ray, Chair
Drinking Water Committee
Science Advisory Board
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EPA-SAB-DWC-95-002
March 1995
An SAB Report: Safe Drinking Water
Future Trends and Challenges
An Environmental Futures Report
by the
Drinking Water Committee of the Science Advisory Board
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Notice
This report has been written as a part of the activities of the SAB, a public advisory group providing
extramural scientific information and advice to the Administrator and other officials of the U.S.
Environmental Protection Agency (EPA). The Board is structured to provide balanced, expert assessment
of scientific matters related to problems facing the Agency. This report has not been reviewed for approval
by the Agency and, hence, the contents of this report do not necessarily represent the views and policies
of the EPA, nor of other agencies in the Executive Branch of the federal government, nor does mention
of trade names or commercial products constitute recommendation for use.
Seven reports were produced from the Environmental Futures Project of the SAB. The titles are
listed below:
(1) Environmental Futures Committee EPA-SAB-EC-95-007
[Title: "Beyond the Horizon: Protecting the Future with Foresight," prepared by the
Environmental Futures Committee of the Science Advisory Board's Executive Committee.]
(2) Environmental Futures Committee EPA-SAB-EC-95-007A
[Title: Futures Methods and Issues, Technical Annex to the Report entitled "Beyond the Horizon:
Protecting the Future with Foresight," prepared by the Environmental Futures Committee of the
Science Advisory Board's Executive Committee.]
(3) Drinking Water Committee EPA-SAB-DWC-95-002
[Title: " Safe Drinking Water: Future Trends and Challenges," prepared by the Drinking Water
Committee, Science Advisory Board.]
(4) Ecological Processes and Effects Committee EPA-SAB-EPEC-95-003
[Title: "Ecosystem Management: Imperative for a Dynamic World," prepared by the Ecological
Processes and Effects Committee, Science Advisory Board.]
(5) Environmental Engineering Committee EPA-SAB-EEC-95-004
[Title: "Review of Environmental Engineering Futures Issues," prepared by the Environmental
Engineering Committee, Science Advisory Board.]
(6) Indoor Air Quality and Total Human Exposure Committee EPA-SAB-IAQC-95-005
[Title: "Human Exposure Assessment: A Guide to Risk Ranking, Risk Reduction and Research
Planning," prepared by the Indoor Air Quality and Total Human Exposure Committee, Science
Advisory Board.]
(7) Radiation Advisory Committee EPA-SAB-RAC-95-006
[Title: "Report on Future Issues and Challenges in the Study of Environmental Radiation, with a
Focus Toward Future Institutional Readiness by the Environmental Protection Agency," prepared
by the Radiation Environmental Futures Subcommittee of the Radiation Advisory Committee,
Science Advisory Board.]
Single copies of any of these reports may be requested and obtained from the SAB, Committee
Evaluation and Support Staff (1400), 401 M Street, SW, Washington, DC 20460 or by FAX (202)
260-1889.
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Abstract
The Environmental Futures Committee (EFC) of the SAB carried out a year-long study to examine
how future developments will affect planning and decision-making for health and environmental quality.
In addition to an overarching "Futures" report by the Executive Committee of the SAB, several standing
committees prepared equivalent reports in their areas of expertise. This report reflects the perspective of
the SAB's Drinking Water Committee.
Emphasizing the fact that freshwater resources are finite, the report first describes major trends in the
availability and quality of drinking water resources in the U.S. The major uses of water are described,
followed by a discussion of four broad factors that will most seriously impact the future of water quality in
the U.S.: a) increased population growth resulting in declining underground water tables and contaminated
water sources; b) increased public demand for cleaner drinking water; c) a changing profile of chemical
and microbial contaminants of concern in drinking water; and d) pressures to fundamentally change the
manner in which drinking water is produced.
The report examines the major challenges that arise from the factors above and makes recommenda-
tions in five areas: a) substantial improvement in the management of water resources, with emphasis on
pollution prevention, recycling, conservation and reallocation of water resources; b) greatly accelerated
research to spur advances in risk assessment methodologies for both chemical and microbial contaminants
of water; c) support for changes in treatment technologies; d) support for the consolidation of small
distribution systems; and, e) establishment of a surveillance or alert system for emerging waterborne
pathogens.
Key Words: Drinking water, future trends, chemical contaminants, microbiological contaminants, risk
assessment, surveillance, water treatment.
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U. S. Environmental Protection Agency
Science Advisory Board
Drinking Water Committee
Chair
Dr. Verne A. Ray
Medical Research Laboratory
Pfizer, Inc.
Groton, CT
Members
Dr. Richard J. Bull
College of Pharmacy
Washington State University
Pullman, WA
Dr. Keith E. Cams
Electric Power Research Institute
Community Environmental Center
Washington State University
Pullman, WA
Dr. Lenore S. Clesceri
Rensselaer Polytechnic Institute
Materials Research Center
Troy, NY
Dr. Anna Fan
State of California
OEHHA/PETS
Berkeley, CA
Dr. Charles Gerba
University of Arizona
Tucson, AZ
Dr. Charles C. Johnson, Jr.
Retired Consultant
Bethesda, MD
Dr. Curtis Klaassen
University of Kansas Medical Center
Kansas City, KS
Dr. Edo D. Pellizzari
Research Triangle Institute
Research Triangle Park, NC
Dr. Richard H. Reitz
McClaren Hart
Flint, MI
in
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Dr. Vernon L. Snoeyink
Department of Civil Engineering
University of Illinois
Urbana, IL
Dr. James M. Symons
Department of Civil and Environmental Engineering
University of Houston
Houston, TX
Dr. Marylynn Yates
University of California
Riverside, CA
Science Advisory Board Staff
Mr. Mauel R. Gomez
Designated Federal Official
Science Advisory Board (1400F)
USEPA
401 M Street, SW
Washington, DC 20460
Ms. Mary Winston
Staff Secretary
Drinking Water Committee
Science Advisory Board (1400F)
USEPA
401 M Street, SW
Washington, DC 20460
IV
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Contents
Page
1. Executive Summary 1
2. Introduction 3
2.1 Background and Charge of Futures Project 3
2.2 Goals and Methodology 3
2.3 Contents of the Report 3
3. Drinking Water Resources: Major Trends in Availability and Quality 4
3.1 Water Resources are Finite 4
3.2 Patterns of Water Use in the U.S 4
3.3 Major Trends and Their Impacts on Future Water Quality 5
3.3.1 Population Growth 5
3.3.1.1 Ground-Water Availability 5
3.3.1.2 Ground-Water Contamination 6
3.3.1.3 Surface Water Availability 6
3.3.1.4 Surface Water Contamination 6
3.3.2 Increased Demand for Clean Water 6
3.3.2.1 Increased Public Awareness and Expectations 6
3.3.2.2 New Knowledge and Lower Detection Levels 7
3.3.2.3 Increased Demand for Protection of Virgin Resources 7
3.3.2.4 Trend for Stricter Standards 7
3.3.2.5 Consolidation of Existing Water Supply Systems 7
3.3.3 Changing Profile of Contaminants of Concern 7
3.3.3.1 Chemical Contaminants 8
3.3.3.2 Microbiological Contaminants 8
4. Future Challenges and Strategies in Management of Water Resources 9
4.1 Water Management 9
4.1.1 Water Resource Allocation Systems 9
4.1.2 Reuse and Conservation 9
4.2 Risk Assessment of Water Contaminants 10
4.2.1 Chemical Contaminants 10
4.2.2 Microbiological Contaminants 10
4.2.3 Strategies to Address Risk Assessment Needs 10
4.3 Design of Treatment and Distribution Systems 11
4.3.1 Technology Changes in the Near Term 11
4.3.2 Technology Changes in the Next 20 Years 12
5. Conclusions and Recommendations 13
6. References R-l
Appendix A A-l
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1. Executive Summary
The Environmental Futures Committee (EFC) of the Science
Advisory Board (SAB) carried out a year-long study to
examine how future developments will affect planning and
future decision-making for health and environmental quality.
In addition to an overarching "Futures" report by the
Executive Committee of the SAB (EPA-SAB EC-95-007),
several standing committees of the SAB prepared a report on
these themes in their areas of expertise.
This report reflects the perspective of the SAB's Drinking
Water Committee (DWC). Its primary goals were to identify
the major trends in drinking water resources and water uses
in the next 5-20 years, to gauge their likely consequences,
and to recommend strategies that would permit the Agency
and the Nation to face the challenges posed by those trends
most effectively.
The amount of freshwater available is finite and humans
everywhere must rely on renewable supplies. For the U.S.,
present and future requirements for safe drinking water will
be governed primarily by population size and patterns of use
of this finite resource. Population growth places severe
demands on drinking water resources through greater
absolute amounts of water needed to support essential human
needs (i.e, drinking water, food supply, power supply),
greater per capita demands that accompany a rising standard
of living and the nature of modern urban society, and
increased contamination burdens from the rising use of finite
water resources to support human activities. Although the
U.S. is a relatively water-abundant country, and its popula-
tion growth modest, current population trends are sufficient
to strain water resources over time, particularly on a regional
basis.
One of the most pervasive and serious problems of the future
is the decline of ground-water tables, on which approxi-
mately 50% of the U.S. population depends for drinking
water. This decline is often related to agricultural uses and
practices and is particularly serious in the western U.S. Much
recent evidence also points to serious contamination of many
underground waters as a result of human activities (e.g., by
nitrates and toxic chemicals), even under optimal conditions
of regulation and technological control.
Industrial development will continue to be an important
focus of concern as a principal source of water contamina-
tion (both underground and surface), although the develop-
ment of effective regulatory strategies to control industrial
discharges (point sources) has reduced the relative impor-
tance of this source of pollution in the last decades. In the
near and long-term nonpoint sources of water pollution will
loom as the greater threat to surface water resources.
Coupled with the increased pressures on water resources,
there has been a growing and increasingly vocal perception
by the public that many drinking water supplies are contami-
nated, and this trend is likely to continue unabated in the
next decades. Increased demands for clean public water
supplies also arise from the discovery of new information on
health effects (e.g., arsenic and lead), from a declining
tolerance on the part of the public to "accept" any health
effects, and from the continually increased ability of analyti-
cal procedures to detect substances in water at lower levels
of concentration. There are also growing expectations for
environmental protection that increasingly demand the
protection of the best natural resources, rather than their
increased use, thus reducing the quantity of resources
available to supply drinking water needs, forcing the use of
resources of lower quality, and increasingly calling upon the
principle of recycling.
All the trends discussed above tend to generate demands for
stricter drinking water standards. The substances that have
been regulated, however, have often been selected without an
adequate evaluation of the true occurrence of those chemi-
cals as contaminants in water.
The chemical contaminants of primary concern in drinking
water today, and in the foreseeable future, arise from the
chemical treatment of water whose goal is to remove the risk
of microbiological hazards. Many of these contaminants can
be measured at increasingly lower concentrations, often
exceeding the ability of scientists to accurately estimate the
human health effects of such low levels of exposure. At the
same time, recent outbreaks of waterborne infectious disease
have focused attention on the shortcomings of current
methods of water treatment, which often do not adequately
eliminate or reduce hazardous microorganisms from treated
waters. These incidents also highlight the need to be ex-
tremely careful when modifying water treatment systems in a
manner that may give rise to new infectious disease risks.
Increasing demands on renewable water resources have
created a need to make tough decisions on how water
resources will be allocated. Competition between uses such
as drinking water, agriculture, fish and wildlife habitats, and
hydroelectric power will increase and greater cooperation
will be required between states and localities that comprise
an area of a given watershed. In order to address these
conflicts, it will be necessary to modify the current State
water allocation systems so that they become more respon-
sive to the trends in resource availability and use described
earlier, and particularly to facilitate increased conservation
and reuse of water. Also, the infrastructure of many U.S.
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water supply systems is old and in need of replacement.
Distribution systems, particularly, will need replacement on
an ever increasing basis throughout the nation. Finally, many
areas of the U.S. are supplied by small and often inefficient
water supply systems that will need to be replaced and
consolidated into larger systems.
The most difficult challenges to the production and delivery
of safe drinking water in the next decades will be in the areas
of evaluating and minimizing the competing risks from
chemical and microbiological contaminants that occur in
water at very low concentrations. Significant advances in
toxicology and epidemiology will be needed to overcome
current gaps in scientific knowledge, including the develop-
ment of a solid biological basis for extrapolation of animal
data to humans, the development of dose-response models
that account for differences in metabolism and pharmacoki-
netics for each chemical, the elucidation of the mechanism
by which each chemical produces its effects and the identifi-
cation of any intrinsic differences in these mechanisms in
animals and humans. In addition, the recognition that the
barriers traditionally used to reduce microbial hazards gives
rise to chemical hazards has focused attention on the fact that
there are currently no well developed and validated methods
to compare microbial to chemical risks. Without such
methods, it is difficult to make decisions that minimize both
types of risk.
A number of likely trends in treatment and distribution
technology are arising as a result of the growing pressures on
drinking water supplies. These include improved filtration
for the elimination of microorganisms, the use of disinfec-
tants other than chlorine, and developments in membrane
treatments. The use of alternative technologies to produce
drinking water may also come into its own in the longer
term, particularly desalination of sea water, which is today
prohibitively expensive.
The Committee recommended: a) improvements in the
existing systems of management of renewable water re-
sources in order to improve quality and increase quantity; b)
substantial acceleration in the research to spur advances in
risk assessment methodologies for both chemical and
microbiological contaminants of water; c) support for
changes in treatment technologies, especially with regard to
disinfection; d) support for the consolidation of small,
inefficient water systems; and, e) the establishment of a
surveillance system for emerging waterborne pathogens.
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2. Introduction
2.1 Background and Charge of Futures
Project
Increasing rates of economic, technological, and societal
change are rapidly transforming the manner in which
government, industry, and consumers grapple with environ-
mental problems and opportunities. A clear understanding of
the dynamics of these changes and the factors that will drive
health and environmental developments and concerns in the
decades ahead is critical to the development of policy
responses that are preventive, focused, and effective. To
assist the Agency in preparing for such future developments
in a rapidly changing world, the Assistant Administrator for
the Office of Policy, Planning and Evaluation (OPPE) at
EPA, David Gardiner, and EPA Administrator Carol
Browner asked the SAB to carry out a study addressing
future environmental and human health problems.
The EFC of the SAB was formed to carry out a year-long
study to examine how future developments will affect
planning and future decision making designed to improve
health and environmental quality. The principal objectives of
the project were to:
a) identify and assess the short- and long-term impacts of
economic, societal, and technological developments
that may affect future health and environmental
quality;
b) investigate methodologies that may guide the planning
efforts of government, industry, and consumers to
anticipate potential adverse health and environmental
impacts from human activities; and
c) select a few key trends to examine with a given
methodology and develop recommendations for
assuming future challenges posed by those trends.
The outcome of this project is an overall report by the SAB's
EFC, together with individual reports by several of the 10
standing committees of the Board, each focusing on future
issues in their areas of expertise. While the deliberations
leading to the individual committee reports played a role in
the overall Futures report of the SAB, they were also
designed to serve as more detailed independent looks at the
future in their respective areas. This report reflects the
perspective of the DWC.
5-20 years, to gauge the likely consequences of those trends,
and to recommend strategies that would permit the Agency
and the Nation to face those future challenges most effec-
tively.
From the beginning, the Committee explicitly chose to
engage in a relatively informal discussion process to meet
these goals and develop its report. Because of constraints of
time and expertise, they did not systematically investigate
the possible use of formal methodologies for futures work of
this type.
Specifically, the DWC initially identified a list of "drivers,"
or factors that in the opinion of the Committee were likely to
dominate developments in the drinking water arena in the
next 5-20 years. A summary of this initial list of factors can
be found in Appendix A. The list was discussed at length,
refined, and the "drivers" were then ranked in importance to
provide a framework for the Committee's report. The
organization and contents of the report reflect the choices
made through this informal methodology.
2.3 Contents of the Report
Following this Introduction, Chapter 3 describes the major
trends in the availability and quality of water resources for
drinking water in the U.S. This includes a description of the
current patterns and trends in water use in the U.S., the major
factors likely to affect the quality of underground and surface
water resources in the near and mid-term, the reasons for an
increased demand in the quality of water, and the resulting
trend for stricter standards and their likely consequences on
treatment and distribution systems. Chapter 4 examines the
implications of these trends in three broad areas that are
critical to the future effective management of water re-
sources; namely, the need for reallocation of water resources,
including the need for more conservation and reuse; the need
for a substantially improved scientific basis for the assess-
ment of both chemical and microbiological risks of drinking
water contaminants; and the likely developments and
changes in treatment and distribution technology. Finally,
Chapter 5 makes a number of recommendations for the
nearer and longer term, based on the analysis developed in
the entire document.
2.2 Goals and Methodology
The primary goals of the report were to identify the major
trends in drinking water resources and water uses in the next
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3. Drinking Water Resources: Major Trends in Availability and Quality1
3.1 Water Resources are Finite
The amount of freshwater available is finite, and humans
everywhere must rely on renewable supplies. For the U.S.
population and the world, present and future requirements
for safe drinking water will be governed primarily by
population size and patterns of use of this finite resource.
Renewable water comes as rain or other precipitation whose
fate may be to seep into the ground, collect in rivers and
lakes, evaporate directly to the atmosphere, or flow back into
the sea from which it is then again drawn by the sun's
energy. In order for this natural hydrologic cycle to be
sustainable, water cannot be taken from reservoirs and other
sources faster than it is replenished. There is essentially no
more freshwater on the planet today than there was thou-
sands of years ago. Water availability calculations indicate a
practical upper limit for the world's available renewable
freshwater (estimated as 9,000-14,000 km3 per year). Not all
of it is available for direct human uses, however, as it is
evident that a substantial proportion of this amount is also
needed to sustain natural ecosystems.
In sharp contrast with the reality of a finite water supply is
the enormous recent increase in world population. World
population doubled between 1940 and 1990, from 2.3 billion
to 5.3 billion human beings, and the per capita use of water
also doubled from 400 to 800 cubic meters (m3) per person
per year. It is unlikely that such a future quadrupling of total
use could be sustained again.
Freshwater availability is determined by climate, including
precipitation and evaporative demand (determined primarily
by average temperature). Further, water availability can vary
widely from season to season and year to year. Among the
greatest single influences on freshwater availability is the
number of people taking from a given resource. Population
growth not only increases direct demands for water, but it
also produces disturbances of the water cycle. Greater needs
for energy and food are often accompanied by trends such as
deforestation and destructive land use practices. Also, higher
standards of living and high density population areas boost
demand for finite regional sources of freshwater (Engleman
and LeRoy, 1993). A comparison by water resource regions
indicates that coastal regions of the U.S. (New England,
Mid-Atlantic, South-Atlantic-Gulf, Pacific Northwest,
California) accounted for nearly one-half of the total water
withdrawn in the U.S. in 1990. In the U.S., each individual is
estimated to use more than 700 liters/day, or 185 gallons for
domestic purposes.
A country whose annual renewable freshwater availability
exceeds about 1700 m3 per person will suffer only occasional
or local water problems (Falkenmark and Widstrand, 1993).
Below this threshold countries begin to experience periodic
or regular water stress. When freshwater availability falls
below 1000 m3 per person per year, countries experience
chronic water scarcity. In the U.S. the total annual renewable
freshwater available is estimated at roughly 2,500,000
million m3. In 1955 a population of 165 million had a per
capita water availability of 14,900 m3. By 1990, with a
population of 250 million, the figure was reduced to 9,900
m3, a drop of 33.6% in 35 years. While this figure suggests
that the U.S. can still be considered a water-abundant
country, the recent rapid decline in per capita availability
does not instill confidence for our future. Further, regional
scarcity of renewable water, such as that experienced in
California in 1987-1992, can produce devastating results to
ecosystems and water quality. Increasing populations in
urban areas and arid sections of the country intensify
shortages of water when drought conditions occur. This will
only be aggravated in future years with continuing popula-
tion growth.
3.2 Patterns of Water Use in the U.S.
Before examining future trends in the availability of water, it
is instructive to briefly review the major uses of water in the
U.S. The U.S. Geological Survey (USGS) conducts an
authoritative survey of water use in the U.S. in 21 water-
resource areas that encompass each state, Puerto Rico, the
U.S. Virgin Islands, and the District of Columbia. The
following quote from the 1990 survey provides a succinct
picture of U.S. water uses:
"Water withdrawals in the U.S. during 1990 were
estimated to average 408,000 million gallons per
day (M gal/d) of freshwater and saline water for
off stream uses2~2% more than the 1985 estimate.
Total freshwater withdrawals were an estimated
' This section is derived mostly from two publications: U.S. Geological
Survey (USGS) Circular 1081 on the estimated uses of water in the U.S. in
1990 (these circulars are prepared at 5-year intervals by USGS) and
Sustaining Water: Population and the Future of Renewable Water Supplies
by Population Action International (1993).
2 Off stream use - water withdrawn or diverted from a ground or surface
water source for public-water supply, industry, livestock, thermoelectric
power generation, and other uses. Sometimes called off-channel use or
withdrawal.
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339,000 M gal/d during 1990, about the same as
during 1985. Average per capita use for all off
stream uses was 1,620 gallons per day (gal/d) of
freshwater and saline water combined and
1,340 gal/d of freshwater. Off stream water-use
categories as used in the USGS Circular 1081 are
classified as public supply, domestic, commercial,
irrigation, livestock, industrial, mining, and
thermoelectric power. During 1990 public-supply
withdrawals were an estimated 35,800 M gal/d,
and self-supplied withdrawals were estimated as
follows: domestic, 3,390 M gal/d; commercial,
2,390 M gal/d; irrigation, 137,000 M gal/d;
livestock, 4,500 M gal/d; industrial, 22,600 M gal/
d, of which 3,270 M gal/d was saline water;
mining, 4,960 M gal/d, of which 1,650 M gal/d
was saline; and thermoelectric power, 195,000 M
gal/d, of which 64,500 M gal/d was saline."
More detailed information from the USGS survey can be
found in Solley et al. (1990). In 1990, freshwater withdraw-
als in the U.S. were 339,000 M gal/d. The four largest use
categories were agricultural irrigation (40.4%), thermoelec-
tric facilities (38.6%), public supplies (11.4%), and industrial
uses (5.7%). Future management and conservation initiatives
in these four use areas, which comprise 96% of freshwater
uses, are the most likely to have favorable impacts in the
availability of water.
3.3 Major Trends and Their Impacts on
Future Water Quality
What factors will most seriously impact the future of water
quality in the U.S.? Four broad factors can be identified: a)
increased population growth resulting in declining under-
ground water tables and contaminated water sources in
general; b) increased public demand for cleaner drinking
water, which will manifest itself in many different ways; c) a
changing profile of contaminants of concern in drinking
water; and d) the resulting pressures to fundamentally
change the manner in which drinking water is produced (i.e.,
lower use of chlorine-containing compounds by industry in
general, and in drinking water in particular). The salient
aspects of each of these factors is discussed in this section, in
terms of both the near term (5 years) and the long term (20
years).
3.3.1 Population Growth
Population growth places multiple and often severe demands
on drinking water resources, as anyone who has resided in a
growth state like California can easily understand. These
demands arise from the greater absolute amounts of water
needed to support essential human needs (i.e., drinking
water, food supply, power supply), greater per capita
demands that accompany a rising standard of living and the
nature of modern urban society, and increased contamination
burdens from the rising use of the water to support myriad
human activities. Although the growth of population in the
U.S. has slowed and is nowhere comparable to the rapid pace
of the developing world, the U.S. rate of growth is sufficient
to strain water resources over time, particularly when the
heterogeneous distribution of population growth is consid-
ered.
The availability of freshwater to meet growing demands
depends upon its regeneration rate. For surface water
sources, such as rivers, it has been estimated that the rate of
regeneration is about 18 days, whereas for large lakes and
deep aquifers it can span thousands of years. Depending
upon the type of hydrogeological formation, ground-water
replenishment may take days to millennia (Engelman and
LeRoy, 1993). In the U.S. the available sources of renewable
water and the issues associated with its use and regeneration
vary considerably across different regions. The growing use
rate of this resource, however, may soon begin to challenge
or exceed the ability for nature to replenish it.
3.3.1.1 Ground-Water Availability
One of the most pervasive and serious problems of the future
is the decline of ground-water tables. This is particularly
important because approximately 50% of the U.S. population
currently depends on underground sources for its drinking
water (Borrelli, 1988). The decline in availability of potable
underground water is often related to agricultural uses and
practices. This phenomenon is especially true for the western
United States, where current trends suggest a severe shortage
of ground water as a source of acceptable source of potable
water in the future.
Some of the unsustainable ground-water use involves
"fossil" aquifers, i.e., underground reservoirs that have held
water hundreds or thousands of years and that receive little
replenishment from rainfall today. These aquifers are
essentially nonrenewable. An example is the large and
important aquifer system in the High Plains (the Ogallala
formation) that stretches from southern South Dakota to
northwest Texas. It has been undergoing depletion for
several decades principally from its heavy use in agriculture.
The High Plains aquifer supplies about 30% of the ground
water used for irrigation in the U.S. The most severe
depletion has occurred in northwest Texas, where heavy
pumping for irrigation began expanding rapidly in the 40s.
As of 1990, 24% of the Texas portion of the Ogallala had
been depleted, a loss equal to nearly six years of the entire
state's water use for all purposes (Brown, 1993). In addition,
pumping costs have risen and irrigation has become uneco-
nomical in northwest Texas (Brown, 1993).
The continued long-term pumping of underground water in
the Sacramento and San Joaquin Valleys of California is
another example of a regional trend towards depletion of
ground-water resources. In this area of the country, intensive
pumping for agricultural, industrial, and domestic use is
leading to intrusion of salt water from the Pacific Ocean,
thereby reducing the water's suitability for drinking in future
years.
Ironically, technological advances in irrigation have also
tended to facilitate large population shifts to arid areas, thus
placing increased pressures on their poor or limited water
resources, especially underground sources. These areas were
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largely inaccessible as large urban habitats until recently.
Also, climatic modelers have been cautiously predicting that
the earth will gradually warm in the years ahead, producing
gradual changes in climatic patterns. For instance, the middle
of North America may slowly grow arid (Milbrath, 1994).
As a result, will extreme weather conditions cause popula-
tion shifts? If so, the consequence may also be important
shifts in the geographical patterns of consumption of
drinking water, with resulting impacts on the future patterns
of regional water scarcity problems.
3.3.1.2 Ground-Water Contamination
In addition to depletion of ground-water resources, much
recent evidence points to serious contamination of many
underground waters as a result of human activities (e.g.,
agriculture, industry, transportation). Increased population
tends to increase these activities and the resulting contamina-
tion, even under optimal conditions of regulation and
technological control. Results from surveys by the USGS
and state agencies of 100,000 wells indicate that for the past
25 years underground sources have become increasingly
polluted by nitrates and other toxic chemicals. Nitrates from
fertilizer use on agricultural crops is common. Excessive
nitrates in wells in areas as diverse as Nebraska, Iowa, and
California's Sacramento Valley have been reported. The
Geological Survey stated that the "Current trends suggest
that nitrate accumulations in ground water of the U.S. will
continue to increase in the future" (Borrelli, 1988). Evidence
has also mounted regarding contamination of underground
aquifers by organic solvents and other hazardous substances
from past waste disposal practices, underground storage
tanks, landfills, and other sources.
3.3.1.3 Surface Water Availability
Surface water availability is also under severe strain in major
areas of the country. A study by the National Academy of
Sciences suggests that water volume in northern California
rivers and the Colorado River will decline by as much as
60% in the future. In the next couple of decades this would
leave much of the West with severe shortages of water. The
frequency of droughts and the danger of major fires would
increase substantially in southern California. The forests
throughout much of the West and upper Midwest would
experience similar incineration (Borrelli, 1988).
On the Atlantic Coast, tide gauges have documented a rise in
sea level of nearly a foot over the past century. Models
predict that the level will have risen by another foot in low-
lying coastal regions of the country in 2030, and by as much
as three feet in 2100. Besides coastal erosion, other threats
posed by a one-to-three-foot rise in sea level include in-
creased salinity of drinking water and saline intrusion into
river deltas and estuaries, which would imperil fisheries
(Borrelli, 1988).
The most easily accessible sources of renewable freshwater
(rivers, streams, lakes, and aquifers) already have been
developed for the three major uses discussed in Chapter 2.
Remaining sources of untapped freshwater supplies available
for mobilization in the U.S. are few, and the cost for devel-
oping less accessible sources will be high. Also, the transport
of water from one river basin to another such as in the
western U.S. is costly (Engleman and LeRoy, 1993).
3.3.1.4 Surface Water Contamination
Industrial development has been and continues to be an
important focus of concern as a principal source of water
contamination (both underground and surface). Yet industrial
development continues to be an important social goal of
virtually every country in the world, including the U.S., and
such development increases with absolute increases in
population and with the increased demand for manufactured
goods that accompanies rising standards of living. In the last
decades, the development of effective regulatory strategies to
control industrial discharges (point sources) has progres-
sively reduced the relative importance of this source of
pollution. Yet increasingly tighter controls in industrial
pollution and pollution prevention incentives will still be
needed and implemented in the future. The second law of
thermodynamics tells us, however, that this battle can only
be won through the expenditure of increasing amounts of
energy.
Nonpoint sources of water pollution, on the other hand, have
been assuming increasing importance as major sources of
water contamination. In the near and long term, this source
of pollution will loom as the greater threat to surface water
resources. The earlier discussion described agricultural
runoffs as important nonpoint sources affecting underground
waters, but agriculture runoffs also severely impact surface
waters, while increased population density in urban areas are
a major source of runoff contamination by heavy metals,
organic chemicals, and other potential chemical hazards.
In summary, increased population is resulting in declining
underground water tables and contaminated water sources in
general. These trends are tangible indications of
unsustainable water use that are increasingly placing water
budgets in the U.S. badly out of balance (Brown, 1993).
3.3.2 Increased Demand for Clean Water
3.3.2.1 Increased Public Awareness and Expectations
In the last decade, there has been a growing perception by
the public that many drinking water supplies are contami-
nated, and this trend is likely to continue unabated in the
next decades. A clear sign of this public perception has been
a marked rise in the use of bottled water throughout the
country. A complete discussion of the reasons for this
perception is beyond the scope of this report, but it is clear
that many of the trends in contamination of surface and
underground waters described in the earlier section were
important determinants of this public attitude. Recent
outbreaks of protozoal, viral, and bacterial disease and
occasional requirements for boiling of water from public
sources have also increased awareness by the public of the
fragile nature of the barrier between safe and contaminated
water supplies.
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3.3.2.2 New Knowledge and Lower Detection
Levels
Increased demands for clean public water supplies also arise
from the discovery of new information on health effects (the
effects of arsenic and lead are current examples with direct
relevance to water), from a declining tolerance on the part of
the public to "accept" any health effects, and from the
continually increased ability of analytical procedures to
detect substances in water at lower levels of concentration.
The latter trend already often exceeds the ability of scientists
to accurately understand and estimate the human health
effects of such low levels of exposure.
3.3.2.3 Increased Demand for Protection of Virgin
Resources
A subtle but important trend in the next decades will also be
that growing expectations for environmental protection will
increasingly demand the protection of the best natural
resources, rather than their increased use. This will reduce
the quantity of resources available to supply drinking water
needs, force the use of resources of lower quality, and
increasingly call upon the principle of recycling to find ways
to make the recycled resources do the job once done with
"virgin" resources.
For example, the Owens River Aqueduct, which supplied
80% of the water to Los Angeles a few years ago, supplies a
much smaller fraction of the city's water today, mostly
because of agreements designed to protect Mono Lake. The
state water project has had its yield substantially reduced in
order to protect certain species in the San Francisco-San
Joaquin Delta. The result is not only water conservation,
water marking, reduced agricultural supplies, and more
traditional wastewater reclamation, but serious consideration
of water supplies for drinking that would not have been
considered in the past. For example, the Metropolitan Water
District of Southern California is seriously studying sea
water desalting and the city of San Diego is now considering
a project involving "indirect potable reuse." The indirect
potable reuse concept includes applying advanced water
treatment to filtered, disinfected secondary effluent and
discharging it into a reservoir that serves as a part of the
supply to the city's drinking water treatment plant. Both of
these alternatives involve the use of sources of water of
originally much poorer quality than those that have tradition-
ally been used. EPA's current regulations are not designed
with water sources of this quality in mind.
3.3.2.4 Trend for Stricter Standards
All the trends discussed above tend to generate demands for
stricter drinking water standards. If properly channeled, these
demands will help to minimize any detrimental public health
impacts of changes in the manner drinking water is obtained
and treated in the future. There are, however, several
troubling patterns in the regulatory arena that could undercut
the potential benefits of future standards.
First, the selection of contaminants to regulate in drinking
water too often has been driven by the identification of those
chemicals that are used in larger volumes on a national scale,
or those chemicals that are perceived as "problems" in the
environment, independent of the true occurrence of those
chemicals as contaminants in water. For example,
rulemaking has been pursued for many persistent pesticides,
PCBs, and dioxins, yet these chemicals are rarely, if ever,
found in drinking water, because of their physical/chemical
characteristics. This type of priority-setting can be very
wasteful of the limited resources of the EPA and the regu-
lated communities.
Secondly, the importance of devising adequate regulatory
strategies will increase dramatically as the proportion of
reused or wastewaters increases in drinking water systems as
a result of diminishing supplies. The character of wastewa-
ters will vary by geographical area, because nonpoint sources
of contamination such as storm water runoff, pesticides that
are mobile in soils, and nitrates will vary by regions. An
effective regulatory strategy will require the flexibility to
take into account these regional variations.
3.3.2.5 Consolidation of Existing Water Supply
Systems
The infrastructure of many U.S. water supply systems is old
and in need of replacement. Distribution systems, particu-
larly, will need replacement on an ever increasing basis in a
significant proportion of towns and cities. Also, many areas
of the U.S. are supplied by small and often inefficient water
supply systems. In the next few years, it is very likely that
the need for massive replacement of many systems, com-
bined with the demands for stricter drinking water standards
described above, will result in the consolidation of many
small systems. Mechanisms to encourage such consolidation
have already been a part of legislative proposals for the
reauthorization of the Safe Drinking Water Act and the
debates surrounding it. Appropriate consolidation of small
systems should improve the overall quality of water and
provide increased revenues to implement water treatment
technologies now available only to larger systems. Larger,
consolidated distribution systems, should also have a
substantial beneficial effect on water quality.
3.3.3 Changing Profile of Contaminants of
Concern
For most of this century and throughout the world, the major
public health goal in the treatment of water prior to its use
for drinking has been to reduce or eliminate the probability
of microbial contamination and thus to prevent waterborne
infectious diseases. The most economical and proven
treatment of water for this purpose involves the use of
reactive chemicals, (particularly different forms of chlorine,
although other chemicals have been used also).
Many of these chemicals, however, have been discovered to
give rise to a variety of by-products when they are used to
disinfect natural waters, and a growing number of these
disinfection by-products are now identified as potential
health hazards to water consumers. For example, there is
substantive epidemiologic and/or toxicological evidence to
suggest that certain by-products of chlorine and ozone, two
common treatment chemicals, may pose risks of cancer and
perhaps other health effects. The degree of risks posed by the
concentrations of these chemicals that are actually found in
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drinking waters, however, are the subject of considerable
controversy. These potentially hazardous by-products arise
from chemical interactions between the natural organic
contaminants of all water sources, particularly surface
waters, and the very reactive nature of the treatment chemi-
cals. Thus, ironically, the chemical contaminants of primary
concern in drinking water today, and in the foreseeable
future, arise from the chemical treatment of water whose
goal is to remove the risk of microbiological hazards.
The following two sections discuss the major factors
affecting the changing profile of chemical and microbial
contaminants of concern in the drinking water arena.
3.3J.I Chemical Contaminants
There are two major and somewhat overlapping sources of
chemical contaminants of concern in drinking water in the
U.S. These are hazardous by-products generated by the
treatment processes, as described briefly above, and the
contaminants from multiple leaching processes from natural
and man-made surfaces mat contact water from the source to
the consumer. With some exceptions, natural contaminants
in source waters, even surface waters, are not typically the
most serious chemical contamination problem. The U.S.
fortunately has had sufficiently plentiful water resources to
allow most sources of drinking-water to be selected with
minimum possibility of chemical and microbial contamina-
tion.
The evaluation of the risks arising from disinfection by-
products is complicated by the increased ability to detect
these by-products in treated waters, an ability that often
outstrips the scientific information and knowledge available
to support accurate and useful risk assessments for them. In
other words, the current state of scientific knowledge often
falls short of what is needed to assess the magnitude of the
hazards posed by these by-products, certainly the degree of
understanding sufficient to design policies that can minimize
chemical risks without raising the competing risks of
waterborne infection. This critical difficulty in grappling
with the risks of water contaminants is discussed in more
detail in the next chapter.
3.3.3.2 Microbiological Contaminants
The microbiological side of the drinking water treatment
scenario is equally critical, however. As the use of traditional
or new chemical treatments is modified to reduce the
generation of hazardous by-products, there is a need to
maintain the efficacy of water treatment plants to minimize
the threat of waterborne disease.
Quite aside from the traditional concern for the disinfection
goals of water treatment plants, a number of recent outbreaks
of waterborne infectious disease (e.g., cholera, and those
attributed to Cryptosporidium, Giardia, E. coli 0157:H7 and
Legionelld) have focused attention on the shortcomings of
current filtration and disinfection components of water
treatment. Although much more scientific data are needed to
draw an accurate picture of the threats posed by these
organisms in U.S. water supplies, it is clear that, at least in
some instances, traditional treatment methods may not
adequately eliminate some of these and possibly other
hazardous microorganisms (e.g., viruses) from treated
waters.
In addition, it is likely that the prevalence of many
waterborne diseases, including those mentioned above, are
woefully underestimated. Several of these diseases may be
having sizable public health impacts because of the large
numbers of people they affect. Also, while most of these
infectious disease threats are unlikely to pose fatal hazards to
healthy individuals, some may be having severe impacts on
more sensitive, weaker, or immunocompromised individuals.
For example, it is projected that from 1980 to 2020, the
number of individuals over 65 will double from 25 to 50
million. Likewise, the number of immunocompromised
individuals is a relatively new and severe problem, magni-
fied by the current AIDS epidemic and escalated by cancer
chemotherapy and organ transplant patients. Not only are
these groups of individuals more susceptible to infection by
waterborne or water-based microorganisms, but they face a
significantly greater risk of severe disease and mortality
from infection than healthy individuals. Thus, the risk of
water-associated illness in the U.S. is likely to increase in the
coming decades. Climate change may also affect the evolu-
tion of new pathogens and their spread through the environ-
ment.
Another area of concern to microbiologists is the possibility
that the profile of microorganisms that grow in water
distribution systems could change to a mix of new and/or
more resistant threats to human health. There are at least two
reasons for this concern. First, changes in water treatment
practices that are triggered by the need to reduce exposure to
toxic disinfection by-products may create new niches for
unrecognized, opportunistic or antibiotic-resistant pathogens
to grow to numbers that increase the risk of illness in
exposed populations. Secondly, the likely overhaul of many
water distribution systems in the next decades with new
materials (e.g., plastic pipes) may also change the habitat
sufficiently for new or modified microorganisms to flourish.
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4. Future Challenges and Strategies in Management of
Water Resources
As described earlier, it can be anticipated that source waters
for the production of drinking water will degrade signifi-
cantly over a 20-year period, as population increases and the
competition for varying uses of water become more intense.
These trends will pose challenges and require new strategies
in the assessment of risks from water contaminants, as well
as in the areas of water resource management, treatment, and
distribution. In brief, these challenges will be, first, a need to
reexamine the character of existing water allocation systems,
shifting their focus from the development of abundant water
resources, to one of increasing conservation and reuse of
those resources. Secondly, there will be demands to substan-
tially improve the scientific basis of the evaluation of the
competing and changing risks of chemical and microbiologi-
cal contamination of drinking water. Thirdly, there will also
be a need to use the results of the improved scientific
knowledge to design treatment and distribution systems that
minimize these risks in a cost-efficient manner.
4.1 Water Management
4.1.1 Water Resource Allocation Systems
Increasing demands on renewable water resources due to
increasing population pressure and other factors have created
a need to make tough decisions on how these water re-
sources will be allocated. Competition between uses such as
drinking water, agriculture, fish and wildlife habitats, and
hydroelectric power will increase and greater cooperation
will be required between states and localities that comprise
an area of a given watershed. For example, competition for
water resources on the Columbia-Snake River system in the
Pacific Northwest, where river-blocking dams have caused
problems with the salmon fisheries, has resulted in several
options, all with potentially severe consequences. These
include a lowering of the Snake River for four months to
natural levels or a drawdown of the Lower Granite Dam for
four months a year. Both would impact fisheries viability,
electric power generation, agriculture, recreational uses,
rights of Indian tribes, and modification of a watershed
affecting irrigation for southern Idaho. This example also
points to the need for a major program of watershed manage-
ment that includes restoration of watersheds, wetland
protection and extension, stabilization of aquatic and
terrestrial areas and provision for safe drinking water.
In order to address these conflicts, it will be necessary to
modify the current state water allocation systems so that they
become more responsive to the trends described in the earlier
chapter, and particularly to facilitate increased conservation
and reuse of water. The current state allocation systems were
typically established in the last century, during an era of
abundant water resources and a need for their development.
They have allocated all the available water, and then some,
to uses such as irrigation, ranching, and mining. Existing
mechanisms to adjust water allocations to the new realities,
such as those of the Snake River System, are woefully
inadequate, and it is necessary to adapt existing policies to
reflect the change from the past era of development of
abundant untapped resources to an era of management of
shrinking available resources.
Any substantial changes in water allocation systems would
be complex and politically difficult to accomplish, however,
as they would have substantial and widespread impact,
particularly throughout the West (Borrelli, 1988).
4.1.2 Reuse and Conservation
As a result of decreasing and deteriorating water resources, it
will also become increasingly necessary to reuse nontradi-
tional sources of water for potable purposes. Reuse of water
will extend to the use of surface waters of less dependable
quality. There will also be pressures for the direct recycling
of wastewater to treatment plants whose product will go
directly to potable water systems, bypassing any intermedi-
ate discharges into water bodies and the consequent partial
natural cleaning processes. While this is not qualitatively
different from current practices-most surface water has been
"used" at some point in the past-the need for faster reuse
cycles will greatly intensify with increased competition for
available supplies of freshwater. The intensity of this need
will vary geographically, but in degree rather than substance.
Finally, as high quality drinking water supplies decrease, it
also will be necessary to apply water conservation practices
more widely and consistently, e.g., lining of irrigation canals,
installation of more efficient plumbing, and consideration of
reallocation of water rights. Conservation will cause big
changes in drinking water systems, however. Lowered
demand for water will mean slower flows and longer
residence times in existing distribution systems, with
attendant quality problems (disinfectant residuals, regrowth,
corrosion, etc.). Also, because of the fixed costs inherent in
water utility operations, water rates per unit volume will
have to be higher in order to raise the necessary revenue.
Although not in the purview of the DWC, the impact of
water conservation on the wastewater collection system and
treatment plant will also need to be addressed.
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The necessary changes in water reuse and conservation will
require public acceptance, and it will be necessary to educate
the public on the various issues facing our society so that the
modified water management strategies can be properly
appreciated and successfully implemented.
4.2 Risk Assessment of Water
Contaminants
4.2.1 Chemical Contaminants
The health impacts of drinking water contaminants depend
on the nature of individual chemicals and their concentra-
tions in drinking water as it is consumed. These concentra-
tions are typically very low, and the current state of scientific
knowledge is often inadequate to accurately estimate
potential health risks that may arise from the resulting low
exposures. The most difficult challenges to the production
and delivery of safe drinking water in the next decades,
therefore, will be in the areas of evaluating and minimizing
the competing risks from chemical and microbiological
contaminants that occur in water at very low concentrations.
Significant advances in toxicology and epidemiology will be
needed to overcome current gaps in scientific knowledge.
In general, it will be necessary to establish a solid biological
basis for extrapolation of animal data to humans for a
relatively select number of chemicals of most immediate
interest, i.e., disinfection by-products. The dose-response
models developed from this effort would explicitly consider
differences in metabolism and pharmacokinetics for each
chemical, the mechanism by which each chemical produces
its effects and any intrinsic differences in these mechanisms
in animals and humans. Much of the human data will have to
be developed using in vitro techniques that have been
validated by in vivo/in vitro comparisons in several species
of experimental animals. In addition to addressing the
questions of direct relevance to drinking water, these efforts
will have the long-term benefit of establishing principles that
will be applicable to the evaluation of other chemicals in a
much more cost-effective way. In turn, this approach will
provide a much more credible means of dealing with
complex mixtures of chemicals that are more typical of
actual human exposure.
The development of more biologically based risk assessment
tools may also change the evaluation of which adverse
effects of chemicals are considered to be most important. For
example, the risks estimated to arise from carcinogens that
act by cytotoxic rather than genotoxic mechanisms will
probably decrease significantly. As calculations of carcino-
genic risk become more biologically based and thus more
realistic, the impact of other effects that are classically
treated as threshold phenomena (e.g., developmental
toxicities) will become more prominent in regulation.
Moreover, it is also possible that the definition of appropriate
safety factors may be found inadequate as knowledge of
those mechanisms that are responsible for such effects are
better defined.
Finally, to support the regulation of disinfection by-products,
the EPA is currently relying on sizable estimates of cancer
risks attributable to the chlorination of drinking water from
the scientific literature (Morris et al., 1992). Some scientists,
however, are skeptical of these estimates, for numerous
reasons (Bull and Kopfler, 1991). In addition, many impor-
tant by-products of chlorination that have not been lexico-
logically characterized are produced by other means of
disinfection, so that shifts away from chlorination to other
methods of disinfection may not successfully reduce carcino-
genic risks.
4.2.2 Microbiological Contaminants
A somewhat different problem exists with risk assessment
for infectious agents. Classically, an estimated degree of risk
has not been explicitly used with microbial agents. Rather,
the effort has depended upon hazard identification and then
installation of general methods of treatment that provide a
series of barriers that reduce or prevent exposure in a
dependable way. The recent recognition that the barriers
traditionally used to reduce microbial hazards give rise to
chemical hazards has focused attention on the shortcomings
of the available methods to compare microbial to chemical
risks such that decisions can be made that result in minimiz-
ing both types of risk.
While the methods for quantifying risks from environmental
exposure to infectious agents are inadequate, they have one
distinct advantage over the estimation of risks from chemical
agents, in that in many cases there is no need to do
interspecies extrapolations. Most of the agents that are of
concern have been clearly shown to produce human disease,
and frequently information is known about how likely
infection is likely to give rise to morbidity and mortality
(Haas, 1993). Moreover, there has been work to actually
document the economic impact in known cases, and this
provides some basis for estimating impact for unreported
cases as well (Payment, 1993). What is generally not known
are actual levels of exposure, the infectious dose for many of
the agents, and how these factors might vary in their impact
with susceptible populations.
4.2.3 Strategies to Address Risk
Assessment Needs
What strategies are available to better address the uncertain-
ties in characterizing and comparing chemical and microbio-
logical risks? The most important strategy in the near and
midterm must be to ensure that sufficient research efforts are
implemented to address the current gaps in toxicologic and
epidemiologic knowledge for both types of contaminants.
Research activities in these two areas must be concurrent and
coordinated by the development of methodologies that can
effectively compare the disparate risks of waterborne disease
and chemical contamination.
The problems posed by disinfection by-products can be
addressed appropriately only after considerably more data
are available to a) verify the currently available
epidemiologic findings; b) establish that the by-products
responsible for the effect are decreased by other forms of
treatment; and c) that other treatments do not give rise to by-
products of comparable health concern.
10
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Unfortunately, the critically needed advances in risk assess-
ment methodologies, as described above, have not been a
priority of regulatory activities to date, and current levels of
publicly funded research are insufficient to address these
needs. If allowed to continue, this trend will have very
damaging consequences.
If sufficient investment in this type of research is not made,
it will be very difficult to articulate directions for the truly
large investments that will be needed to improve drinking
water treatment and distribution systems and accommodate
anticipated population increases over the next two decades.
Many current distribution systems are more than 100 years
old and due for replacement or major repairs. To a lesser
extent, many treatment plants are also due for replacement in
the U.S. Treatment plants must consider a productive
lifetime of at least 25-50 years, and local authorities will find
it increasingly difficult to obtain financial resources in the
face of scientific uncertainty about potential risks and
uncertain standards that could make sizable investments
obsolete in a few years. Moreover, regulation of chemicals
whose risks cannot be clearly documented with scientific
evidence will tend to undermine public confidence in the
process for setting drinking water standards.
4.3 Design of Treatment and
Distribution Systems
The combined pressures of population and growing demands
for cleaner drinking water were discussed in Chapter 3. The
critical need for a solid scientific basis to address the
consequences of these pressures and to guide investments in
water treatment facilities over the next two decades was
discussed above. Despite the gaps in scientific knowledge,
however, a number of likely trends in treatment and distribu-
tion technology are already arising as a result of these
pressures. The more likely technological developments in the
near and midterm are discussed in Section 4.3.1 below.
Treatment changes in the more distant future are discussed in
Section 4.3.2.
4.3.1 Technology Changes in the Near
Term
The primary goals for changes in treatment and distribution
systems in the next decade will be to improve microbial
safety, control corrosivity, and lower concentrations of
disinfection by-products. Unfortunately, these goals are
somewhat in conflict. For example, disinfection is improved
at low pH and in the presence of higher concentrations of
disinfectants. In contrast, low pH aggravates corrosivity and
high concentrations of disinfectant create more disinfection
by-products.
Treatment changes will be required to improve filtration
such that it will remove some of the more difficult to
inactivate microorganisms such as Giardia and
Cryptosporidum. This will allow disinfection using lower
concentrations of disinfectants. Disinfection by-products will
be controlled through the removal of precursors by improv-
ing coagulation, or adding adsorption, oxidation, or mem-
branes as unit processes beyond "conventional" treatment.
This will allow the use of lower concentrations of disinfec-
tant to provide adequate disinfection and the use of high pH
to meet the requirements of the "lead and copper" rule.
Two common disinfectants do not use chlorine or chlorine-
containing products, ozone and ultraviolet radiation. Both
will probably be employed more frequently. Because neither
produces a disinfectant residual for distribution system
protection, however, a small amount of chlorine or chlorine-
based material will continue to be needed to maintain
protection of the public. Another approach to biofilm control
in distribution systems involves the removal of biodegrad-
able organic matter in the treatment plant. This will lower the
demand for biocide in the distribution system, thus saving on
the use of chlorine and its compounds.
The final area of near-term changes relates to improvement
of ground-water quality. Many ground waters have been
contaminated by solvents and other organic compounds. As
clean-up and restoration activities increase, the challenge to
the water utilities may ease somewhat, although there will be
increased pressures from growing runoff (nonpoint) sources
of contamination.
Of course, the development of technology makes higher
environmental standards and higher standards of living
possible, at least, if the energy to drive our technological
processes become more available in the future. Technologi-
cal development is the only hope we have for resolving the
seeming conflict between our goal of having more people
living better while trying to reduce the adverse impact we
have on the environment at the same time.
In summary, the most important foreseeable developments in
the technology area in the near and midterm are the follow-
ing:
a) Membrane treatment as a substitute for both
conventional filtration and primary disinfection
using oxidants.
b) Membrane treatment as a more effective means of
removing natural and synthetic organics from
drinking water.
c) The elimination of metallic materials in distribution
systems and consumer plumbing.
d) The development of methods for stabilizing water
in distribution systems that do not depend on
maintenance of a residual oxidant in the distribution
system.
e) The development of additional strategies to protect
membrane disinfected water from contamination
during distribution (cross connection control, higher
pressure standards, etc.).
f) The development of methods for real-time assess-
ment of microbiological contaminants and/or
particulates, including a number of important
pathogens.
g) The development of more sophisticated methods for
maintaining high water quality during storage in
large distribution system reservoirs.
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4.3.2 Technology Changes in the Next 20
Years
Treatment changes in the more distant future (20 years) are
far more difficult to discuss. The treatment technologies that
are selected to minimize chemical and microbiological
hazards will be decided by the results of the accelerated
scientific research in risk assessment recommended in
Section 4.1.2 above. Unit processes not yet developed will
be competing with conventional treatments for future use.
Moreover, developments in two other areas also will
undoubtedly occur, however, both of which will influence
drinking water: pollution prevention technology and conser-
vation.
The movement by industry, agriculture, and municipal water
and wastewater treatment plants to lower the quantities of
their residuals and to recycle them will cause long-range
improvements in source water quality. This improvement
will lower the pressure on water utilities to continually
increase the aggressiveness of treatment to prevent health
risks and allow more attention to the production of a quality
product, pleasant to the consumer in every way.
Conservation, which was discussed in Section 4.1.2, will
also result in changes in cost and quality of drinking water
systems, as well as in potential detrimental impacts on
wastewater collection system and treatment plants.
Another strategy that will become increasingly available in
the next decades will be the use of alternative technologies to
produce drinking water. Desalination of sea water, a theoreti-
cally sustainable source of freshwater, is one example. It is
high in capital and energy costs, generally several times
more than water supplied by conventional means. The
current major constraint of desalination is the need to use
fossil fuels, with their finite supply and contribution to air
pollution. Future energy technologies have the potential of
being clean, inexhaustible and inexpensive, and therefore
may make the pursuit and application of alternative tech-
nologies feasible.
The new energy technologies are typically high-tech,
industrialized power generation ranging from nuclear fission
and nuclear fusion to the large-scale capture of solar energy.
For nuclear fission, the answer is breeder reactors to generate
power and atomic fuel, although few experts now see this as
an option beyond the year 2025 (Garbarino, 1992). For
nuclear fusion the key is to find a way to transform globally
abundant hydrogen into usable energy. Ohkawa, vice
president for fusion power research at Gulfs General Atomic
Company, says that research programs could lead to con-
struction of an experimental fusion reactor within a decade
(Garbarino, 1992). Cetron (1994) has predicted that fusion
reactors producing "clean" nuclear energy will appear after
2010; by 2030 they will be a major source of power. He also
predicts that ocean-wave power plants will produce both
electricity and freshwater for island communities.
A final observation concerns the effect of technophobia or
fear of technology. Technology, particularly chemistry, will
continue to be a mystery to the public and, as a result, the
public will continue to put pressure on the EPA and on
Congress to find-fail safe solutions to problems where only
judgments of relative risk can be made. Attempts to balance
risk and cost will continue to be viewed as an effort to avoid
environmental responsibility. Congress will continue to be
frustrated with progress in regulation. Only if the Adminis-
tration works closely and effectively with Congress, the
industry, and the public will a sensible outcome occur.
A wise person once said, "Predictions are always difficult,
particularly when they are about the future." Thus, looking
five years ahead is risky, but less uncertain, as some of the
forces currently in motion will come to fruition in that time
frame. A 20-year time line is much more difficult because of
unexpected surprises. Looking back 20 years, trihalomethanes
were just being discovered, and their impact was totally
unpredictable.
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5. Conclusions and Recommendations
The major challenges facing the future provision of safe
drinking water in the U.S. will be the increased demands on
finite water resources and the need to minimize the risks
posed by both chemical and microbiological contaminants.
These challenges have implications for changes in the
management of water resources and for changes that are
made to existing drinking water treatment and distribution
systems. The Committee's major recommendations in these
areas are:
a) Improve the existing systems of management of
renewable water resources. Greater emphasis
must be given to improving the management of
existing renewable water supplies. A national
management program should include 1) prevention
of further water supply deterioration, including
pollution prevention and better management of
land-use and forestry practices; 2) improvement of
our ability to capture a larger proportion of renew-
able water supplies, including wetland protection
and extension; and 3) implementation of water
recycling and conservation practices to improve
efficiencies of water use, including lining of
irrigation canals, installation of more efficient
plumbing, and consideration of reallocation of
water rights.
b) Greatly accelerate research to spur advances in
risk assessment methodologies for both chemical
and microbiological contaminants of water.
Modifications of current water disinfection treat-
ments to minimize chemical risks in the drinking
water supply must consider the magnitude of
microbial risks that may be introduced as a result of
the changes, as well as the creation of other
disinfection by-products. To do this effectively,
substantial research into risk assessment methodol-
ogy for both chemical and microbial risks is
urgently needed. This research must emphasize a
more biologically based risk assessment process in
order to determine what adverse effects of chemi-
cals are most important. Without the understanding
that will come about from such research, large
public investments for changes in drinking water
treatment plants may be made on an inadequate and
possibly incorrect scientific basis.
c) Support changes in treatment technologies. The
trends that were discussed in the earlier sections of
this report will cause the concepts of water treat-
ment and distribution to change in the future, both
in the near term (5 years) and the longer term
(20 years or more).
In treatment systems, technological developments
that will need to be improved and implemented will
include membrane treatment as a substitute for both
conventional filtration and primary disinfection
using oxidants. Membrane treatment will also be
considered as a more effective means of removing
natural and synthetic organics from drinking water.
In addition, methods will need to be developed for
stabilizing water in distribution systems that do not
depend on maintenance of a residual oxidant in the
distribution system.
There will also arise new strategies to ensure
adequate future water supplies, particularly im-
provements in the economic efficiency of desalina-
tion of sea water. However, such a process will
require a cheaper source of power or energy. New
energy technologies ranging from nuclear fission
and nuclear fusion to the large-scale capturing of
solar energy may develop to the point of making
desalination more economically feasible.
d) Support the consolidation of small distribution
systems. A greater consolidation of small systems
should occur that will improve the overall quality of
water and provide the necessary revenue to imple-
ment treatment technologies now available to the
larger systems. The drive toward consolidation
should take advantage of the replacement of
distribution systems that will be necessary in the
near future in many communities.
e) Establish a surveillance or alert system for
emerging waterborne pathogens. The almost
certain changes in water treatment and distribution
systems in the next decades and the increased
consolidation into larger and large systems for
efficiency of control and delivery of water poses the
very real danger of the generation and transmission
to large populations of heretofore unknown micro-
organisms that may pose serious disease threats. A
surveillance or alert system to detect these threats
early should be put in place.
13
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6. References
Borrelli, P. 1988. Crossroads: Environmental Priorities for Haas, C.N. 1993. Quantifying Microbial Risk. In: Craun,
the Future. Island Press, Washington, D.C./Covelo, CA. G.F., ed. Safety of Water Disinfection: Balancing
Chemical and Microbial Risks. ILSI Press, Washington,
Brown, L.R. 1993. Vital Signs 1993: The Trends That are Dc np 389-398
Shaping Our Future. World Watch Institute.
Milbrath, L.W. 1994. Climate and Chaos: Societal Impacts
Bull, R.J. and F.C. Kopfler. 1991. Health Effects of Disin- of Sudden Weather shifts The Futurist 28(3):26.
fectants and Disinfection By-Products. American Water
Works Association and AWWA Research Foundation, Morris, R.D., A.-M. Audet, J.F. Angelillo, T.C. Chalmers,
Denver, CO. and F. Mosteller. 1992. Chlorination, chlorination by-
products, and cancer A meta-analysis. Am. J. Public
Cetron, M. 1994. 74 Trends That Will Affect America's Health 82-955-963
Future - and Yours. The Futurist. 28(2):9.
Payment, P. 1993. Viruses: Prevalence of Disease, Levels
Engleman, R. and P. LeRoy. 1993. Sustaining Water: ^ Sources In; Craun> G F ed Safe{y ofWater
Population and the Future of Renewable Water Disinfection: Balancing Chemical and Microbial Risks.
Supplies. Population Action International. Washington, ^ Press> Washington) D.C., pp 99-113.
DC.
Solley, W.B., R.R. Pierce, and H.A. Perlman. 1990. Esti-
Falkenmark, M. and C. Widstrand. 1992. Population and maed Use ofWater in the United Stafes in mo y s
Water Resources: A Delicate Balance. Population Geological Survey Circular 1081. Washington, DC.
Bulletin. Population Reference Bureau.
Garbarino, J. 1992. Toward a Sustainable Society: An
Economic Social and Environmental Agenda for our
Childrens' Future. The Noble Press. Chicago, IL.
R-1
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Appendix A
List of Factors That Formed the Initial Basis of the
Committee's Discussion
1. Water supply/demand issues.
2. Environmental protection vs. human uses/needs.
3. Economics, cost of water.
4. Costs to states and communities of regulatory "overload."
5. Use of bottled water, contamination and regulation.
6. Reuse of water.
7. Increase in immunocompromised individuals and resistant organisms.
8. Aging of water system infrastructures.
9. Use of water as garbage disposal vehicle.
10. Ground-water contamination.
11. Use of membrane technology for water purification.
12. Use of salt water, desalination.
13. Dual systems of water delivery (potable, nonpotable).
14. Population shifts and dynamics.
15. Limits on construction and development.
16. Possible shifts away from large urban concentrations.
17. Possible trends towards greater population density with increasing transportation fuel costs.
18. Source protection as a trend.
19. Greater use of networks, as for electrical systems, to shift water resources around country.
20. Use of cisterns and rainwater and solar disinfection.
21. Decreased use of pesticides.
22. Possible increased use of tilled land.
23. Increased demands on water supply if any efforts to re-industrialize.
A-1
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