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Summary As the world enters the 21st century, the human County Water District, the Orange County Sanitation community finds itself searching for new paradigms District, the Los Angeles Department of Water and for water supply and management. As communities Power, the Irvine Ranch Water District, the West Basin face water supply challenges amidst continued popula- Water District, the Inland Empire Utilities Agency, the tion growth and climate change, water reuse, or the Metropolitan Water District of Southern California, use of highly treated wastewater effluent (also called the Los Angeles County Sanitation Districts, and the reclaimed water) for either potable or nonpotable Monterey Regional Water Pollution Control Agency. purposes, is attracting increasing attention. Many com- In this report, the committee analyzes technical, munities have implemented inexpensive water reuse economic, institutional, and social issues associated projects, such as irrigating golf courses and parks or with increased adoption of water reuse and provides an providing industrial cooling water in locations near updated perspective since the NRC’s last report, Issues the wastewater reclamation plant. In the process, these in Potable Reuse (NRC, 1998). This report considers communities have become familiar with the advantages a wide range of reuse applications, including drinking of water reuse, such as improved reliability and drought water, nonpotable urban uses, irrigation, industrial resistance of the water supply. However, increased use process water, groundwater recharge, and ecological of reclaimed water typically poses greater financial, enhancement. technical, and institutional challenges than traditional sources and some citizens are concerned about the CONTEXT AND POTENTIAL safety of using reclaimed water for domestic purposes. FOR WATER REUSE These challenges have limited the application of water Municipal wastewater reuse offers the potential reuse in the United States. to significantly increase the nation’s total available The National Research Council’s (NRC’s) Com- water resources. Approximately 12 billion gallons of mittee on Assessment of Water Reuse as an Approach for Meeting Future Water Supply Needs was formed municipal wastewater effluent is discharged each day to conduct a comprehensive study of the potential for to an ocean or estuary out of the 32 billion gallons water reclamation and reuse of municipal wastewater per day discharged nationwide. Reusing these coastal to expand and enhance the nation’s available water sup- discharges would directly augment available water ply alternatives (see Box S-1 for the statement of task). resources (equivalent to 6 percent of the estimated total U.S. water use or 27 percent of public supply).1 The study is sponsored by the Environmental Protec- tion Agency, the Bureau of Reclamation, the National W hen reclaimed water is used for nonconsumptive Science Foundation, the National Water Research Institute, the Centers for Disease Control and Pre- 1 See Chapter 1 for details on how the committee calculated this vention, the Water Research Foundation, the Orange discharge total and the percentages. 1
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2 WATER REUSE BOX S-1 Statement of Task A National Research Council committee, convened by the Water Science and Technology Board, conducted a comprehensive study of the potential for water reclamation and reuse of municipal wastewater to expand and enhance the nation’s available water supply alternatives. The committee was tasked to address the following issues and questions: 1. Contributing to the nation’s water supplies. What are the potential benefits of expanded water reuse and reclamation? How much municipal wastewater effluent is produced in the United States, what is its quality, and where is it currently discharged? What is the suitability—in terms of water quality and quantity—of processed wastewaters for various purposes, including drinking water, nonpotable urban uses, irrigation, industrial processes, groundwater recharge, and environmental restoration? 2. Assessing the state of technology. What is the current state of the technology in wastewater treatment and production of reclaimed water? How do available treatment technologies compare in terms of treatment performance (e.g., nutrient control, contaminant control, pathogen removal), cost, energy use, and environmental impacts? What are the current technology challenges and limitations? What are the infrastructure requirements of water reuse for various purposes? 3. Assessing risks. What are the human health risks of using reclaimed water for various purposes, including indirect potable reuse? What are the risks of using reclaimed water for environmental purposes? How effective are monitoring, control systems, and the existing regulatory framework in assuring the safety and reliability of wastewater reclamation practices? 4. Costs. How do the costs (including environmental costs, such as energy use and greenhouse gas emissions) and benefits of water reclamation and reuse generally compare with other supply alternatives, such as seawater desalination and nontechnical options such as water conservation or market transfers of water? 5. Barriers to implementation. What implementation issues (e.g., public acceptance, regulatory, financial, institutional, water rights) limit the applicability of water reuse to help meet the nation’s water needs and what, if appropriate, are means to overcome these challenges? Based on a consideration of case studies, what are the key social and technical factors associated with successful water reuse projects and favorable public attitudes toward water reuse? Conversely, what are the key factors that have led to the rejection of some water reuse projects? 6. Research needs. What research is needed to advance the nation’s safe, reliable, and cost-effective reuse of municipal wastewater where traditional sources of water are inadequate? What are appropriate roles for governmental and nongovernmental entities? uses, the water supply benefit of water reuse could be ties, practitioners, and regulatory authorities. The use of even greater if the water can again be captured and reclaimed water to augment potable water supplies has reused. Inland effluent discharges may also be avail- significant potential for helping to meet future needs, able for water reuse, although extensive reuse has the but planned potable water reuse only accounts for a potential to affect the water supply of downstream users small fraction of the volume of water currently being and ecosystems in water-limited settings. Water reuse reused. However, potable reuse becomes more signifi- alone cannot address all of the nation’s water supply cant to the nation’s current water supply portfolio if de facto (or unplanned) water reuse2 is included. T he de challenges, and the potential contributions of water facto reuse of wastewater effluent as a water supply is reuse will vary by region. However, water reuse could common in many of the nation’s water systems, with offer significant untapped water supplies, particularly in coastal areas facing water shortages. Water reuse is a common practice in the United 2 De facto reuse is defined by the committee as a drinking water States. Numerous approaches are available for reusing supply that contains a significant fraction of wastewater effluent, typically from upstream wastewater discharges, although the water wastewater effluent to provide water for industry, irri- supply has not been permitted as a water reuse project. There is no gation, and potable supply, among other applications, specific cutoff for how much effluent in a water source is considered although limited estimates of water reuse suggest that de facto reuse, because water quality is affected by the extent of it accounts for a small part (<1 percent) of U.S. water instream contaminant attenuation processes and travel time. How- ever, water supplies where effluent accounts for more than a few use. Water reclamation for nonpotable applications is percent of the overall flow are usually considered to be undergoing well established, with system designs and treatment de facto reuse. For a detailed discussion of the extent of effluent technologies that are generally accepted by communi- contributions to water supplies, see Chapter 2.
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3 SUMMARY some drinking water treatment plants using waters in reclaimed water, facilitating a multitude of process from which a large fraction originated as wastewater combinations that can be tailored to meet specific wa- effluent from upstream communities, especially un- ter quality objectives. Advanced treatment processes der low-flow conditions. are also capable of addressing contemporary water An analysis of the extent of de facto potable quality issues related to potable reuse involving emerg- water reuse should be conducted to quantify the ing pathogens or trace organic chemicals. Advances number of people currently exposed to wastewater in membrane filtration have made membrane-based contaminants and their likely concentrations. A processes particularly attractive for water reuse applica- systematic analysis of the extent of effluent contribu- tions. However, limited cost-effective concentrate dis- tions to potable water supplies has not been made in posal alternatives hinder the application of membrane the United States for over 30 years. Such an analysis technologies for water reuse in inland communities. Natural systems are employed in most potable would help water resource planners and public health water reuse systems to provide an environmental agencies understand the extent and importance of de buffer. However, it cannot be demonstrated that facto water reuse. such “natural” barriers provide any public health protection that is not also available by other engi- WATER QUALITY AND WASTEWATER neered processes (e.g., advanced treatment processes, RECLAMATION TECHNOLOGY reservoir storage). Environmental buffers in potable The very nature of water reuse suggests that nearly reuse projects may fulfill some or all of three design any substance used or excreted by humans has the elements: (1) provision of retention time, (2) attenu- potential to be present at some concentration in the ation of contaminants, and (3) blending (or dilution). treated product. Modern analytical technology allows However, the extent of these three factors varies widely detection of chemical and biological contaminants at across different environmental buffers under differ- levels that may be far below human and environmental ing hydrogeological and climatic conditions. In some health relevance. Therefore, if wastewater becomes cases engineered natural systems, which are generally part of a reuse scheme (including de facto reuse), the perceived as beneficial to public acceptance, can be impacts of wastewater constituents on intended ap- substituted for engineered unit processes, although the plications should be considered in the design of the science required to design for uniform protection from treatment systems. Some constituents, such as salinity, one environmental buffer to the next is not available. sodium, and boron, have the potential to affect agri- The lack of clear and standardized guidance for design cultural and landscape irrigation practices if they are and operation of engineered natural systems is the big- present at concentrations or ratios that exceed specific gest deterrent to their expanded use, in particular for thresholds. Some constituents, such as microbial patho- potable reuse applications. gens and trace organic chemicals, have the potential to affect human health, depending on their concentration QUALITY ASSURANCE and the routes and duration of exposure (see Chapter Reuse systems should be designed with treat - 6). Additionally, not only are the constituents them- ment trains that include reliability and robustness. selves important to consider but also the substances into which they may transform during treatment. Redundancy strengthens the reliability of contaminant Pathogenic microorganisms are a particular focus of removal, particularly important for contaminants with water reuse treatment processes because of their acute acute affects, while robustness employs combinations human health effects, and viruses necessitate special of technologies that address a broad variety of con- attention based on their low infectious dose, small size, taminants. Reuse systems designed for applications and resistance to disinfection. with possible human contact should include redundant A portfolio of treatment options, including engi- barriers for pathogens that cause waterborne diseases. neered and managed natural treatment processes, ex- Potable reuse systems should employ diverse processes ists to mitigate microbial and chemical contaminants that can function as barriers for many types of chemi-
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4 WATER REUSE cals, considering the wide range of physiochemical potable water reuse projects. However, environmental properties of chemical contaminants. buffers are not essential elements to achieve quality Reclamation facilities should develop monitor- assurance in potable reuse projects. Additionally, the ing and operational plans to respond to variability, classification of potable reuse projects as indirect (i.e., e quipment malfunctions, and operator error to includes an environmental buffer) and direct (i.e., does ensure that reclaimed water released meets the ap- not include an environmental buffer) is not productive propriate quality standards for its use. Redundancy from a technical perspective because the terms are not and quality reliability assessments, including process linked to product water quality. control, water quality monitoring, and the capacity to divert water that does not meet predetermined quality UNDERSTANDING THE RISKS targets, are essential components of all reuse systems. Health risks remain difficult to fully characterize A key aspect involves the identification of easily mea- and quantify through epidemiological or toxicologi- sureable performance criteria (e.g., surrogates), which cal studies, but well-established principles and pro- are used for operational control and as a trigger for cesses exist for estimating the risks of various water corrective action. reuse applications. Absolute safety is a laudable goal Monitoring, contaminant attenuation processes, post-treatment retention time, and blending can be of society; however, in the evaluation of safety, some effective tools for achieving quality assurance in both degree of risk must be considered acceptable (NAS, nonpotable and potable reuse schemes. Today most 1975; NRC, 1977). To evaluate these risks, the prin- projects find it necessary to employ all these elements, ciples of hazard identification, exposure assessment, and different configurations of unit processes can dose-response assessment, and risk characterization achieve similar levels of water quality and reliability. In can be used, as outlined in Chapter 6. Risk assessment the future, as new technologies improve capabilities screening methods enable estimates of potential human for both monitoring and attenuation, it is expected health effects for circumstances where dose-response that retention and blending requirements currently data are lacking. Although risk assessment will be an imposed on many potable reuse projects will become important input in decision making, it only forms one less significant in quality assurance. of several such inputs, and risk management decisions The potable reuse of highly treated reclaimed incorporate a variety of other factors, such as cost, water without an environmental buffer is worthy of equitability, social, legal and regulatory factors, and consideration, if adequate protection is engineered qualitative public preferences. within the system. Historically, the practice of adding The occurrence of a contaminant at a detectable level does not necessarily pose a significant risk. In- reclaimed water directly to the water supply without an environmental buffer—a practice referred to as direct stead, only by using dose-response assessments can a potable reuse—has been rejected by water utilities, by determination be made of the significance of a detect- regulatory agencies in the United States, and by previ- able and quantifiable concentration. A better understanding and a database of the ous NRC committees. However, research during the performance of treatment processes and distribu- past decade on the performance of several full-scale tion systems are needed to quantify the uncertainty advanced water treatment operations indicates that in risk assessments of potable and nonpotable water some engineered systems can perform equally well reuse projects. Failures in reliability of a water reuse or better than some existing environmental buffers in diluting and attenuating contaminants, and the treatment and distribution system may cause a short- proper use of indicators and surrogates in the design term risk to those exposed, particularly for acute con- of reuse systems offers the potential to address many taminants (e.g., pathogens) where a single exposure concerns regarding quality assurance. Environmental is needed to produce an effect. To assess the overall buffers can be useful elements of design that should risks of a system, the performance (variability and be considered along with other processes and man- uncertainty) of each of the steps needs to be under- agement actions in formulating the composition of stood. Although a good understanding of the typical
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5 SUMMARY performance of different treatment processes exists, an For example, disinfection byproducts, in particular improved understanding of the duration and extent of nitrosodimethylamine (NDMA), and perfluorinated any variations in performance at removing contami- chemicals deserve special attention in water reuse nants is needed. projects because they represent a more serious human When assessing risks associated with reclaimed health risk than do pharmaceuticals and personal care water, the potential for unintended or inappropriate products. Despite uncertainties inherent in the analy- uses should be assessed and mitigated. If the risk is sis, these results demonstrate that following proper then deemed unacceptable, some combination of more diligence and employing tailored advanced treatment stringent treatment barriers or more stringent controls trains and/or natural engineered treatment, potable against inappropriate uses would be necessary if the reuse systems can provide protection from trace organic project is to proceed. Inadvertent cross connection contaminants comparable to what the public experi- of potable and nonpotable water lines represent one ences in many drinking water supplies today. With respect to pathogens, although there is a t ype of unintended outcome that poses significant great degree of uncertainty, the committee’s analysis human health risks from exposure to pathogens. To suggests the risk from potable reuse does not appear significantly reduce the risks associated with cross to be any higher, and may be orders of magnitude connections, particularly from exposure to pathogens, lower, than currently experienced in at least some nonpotable reclaimed water distributed to communi- current (and approved) drinking water treatment ties via dual distribution systems should be disinfected systems (i.e., de facto reuse). State-of-the-art water to reduce microbial pathogens to low or undetectable levels. Enhanced surveillance during installation of treatment trains for potable reuse should be adequate to reclaimed water pipelines may be necessary for non- address the concerns of microbial contamination if fin- potable reuse projects that distribute reclaimed water ished water is protected from recontamination during that has not received a high degree of treatment and storage and transport and if multiple barriers and qual- disinfection. ity assurance strategies are in place to ensure reliability of the treatment processes. The committee’s analysis is presented as an exemplar (see Appendix A for details EVALUATING THE RISKS OF and assumptions made) and should not be used to POTABLE REUSE IN CONTEXT endorse certain treatment schemes or determine the It is appropriate to compare the risk of water risk at any particular site without site-specific analyses. produced by potable reuse projects with the risk as- sociated with the water supplies that are presently in ECOLOGICAL APPLICATIONS use. In Chapter 7, the committee presents the results OF WATER REUSE of an original comparative analysis of potential health Currently, few studies have documented the en- risks of potable reuse in the context of the risks of a vironmental risks associated with the purposeful use conventional drinking water supply derived from a of reclaimed water for ecological enhancement. Wa- surface water that receives a small percentage of treated wastewater. By means of this analysis, termed a risk ex- ter reuse for the purpose of ecological enhancement is a emplar, the committee compares the estimated risks of relatively new and promising area of investigation, but a common drinking water source generally perceived as few projects have been completed and the committee safe (i.e., de facto potable reuse) against the estimated was unable to find any published research in the peer- risks of two other potable reuse scenarios. reviewed literature investigating potential ecological The committee’s analysis suggests that the risk effects at these sites. As environmental enhancement from 24 selected chemical contaminants in the two projects with reclaimed water increase in number and potable reuse scenarios does not exceed the risk in scope, the amount of research conducted with respect common existing water supplies. The results are help- to ecological risk should also increase, so that the po- ful in providing perspective on the relative importance tential benefits and any issues associated with the reuse of different groups of chemicals in drinking water. application can be identified.
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6 WATER REUSE The ecological risk issues and stressors in eco- far from the water reclamation plant, the total costs of logical enhancement projects are not expected to nonpotable projects can be significantly greater than exceed those encountered with the normal surface potable reuse projects, which do not require separate water discharge of municipal wastewater. Further, distribution lines. Although each project’s costs are site specific, the presence of contaminants and potential ecological comparative cost analyses suggest that reuse projects impacts may be lower if additional levels of treatment tend to be more expensive than most water conserva- are applied. The most probable ecological stressors in- tion options and less expensive than seawater desali- clude nutrients and trace organic chemicals, although nation. The costs of reuse can be higher or lower than stressors could also include temperature and salinity brackish water desalination, depending on concentrate under some circumstances. For some of these potential disposal and distribution costs. Water reuse costs are stressors (e.g., nutrients), there is quite a bit known typically much higher than those for existing water about potential ecological impacts associated with sources. The comparative costs of new water storage exposure. Less is known about the ecological effects of alternatives, including groundwater storage, are widely trace organic chemicals, including pharmaceuticals and variable but can be less than those for reuse. personal care products, even though aquatic organisms To determine the most socially, environmentally, can be more sensitive to these chemicals than humans. and economically feasible alternative, water manag- Sensitive ecosystems may necessitate more rigorous ers and planners should consider nonmonetized costs analysis of ecological risks before proceeding with and benefits of reuse projects in their comparative ecological enhancement projects with reclaimed water. cost analyses of water supply alternatives. Water reuse projects offer numerous benefits that are frequently COSTS not monetized in the assessment of project costs. For Financial costs of water reuse are widely variable example, water reuse systems used in conjunction with a because they are dependent on site-specific factors. water conservation program can be effective in reducing seasonal peak demands on the potable system, which F inancial costs are influenced by size, location, in- reduces capital and operating costs and prolongs exist- coming water quality, expectations and/or regulatory ing drinking water resources. Water reuse projects can requirements for product water quality, treatment train, also offer improved reliability, especially in drought, method of concentrate disposal, extent of transmission and can reduce dependence on imported water supplies. lines and pumping requirements, timing and storage Depending on the specific designs and pumping re- requirements, costs of energy, interest rates, subsidies, quirements, reuse projects may have a larger or smaller and the complexity of the permitting and approval carbon footprint than existing supply alternatives. They process. Capital costs in particular are site specific and can also reduce water flows to downstream users and can vary markedly from one community to another. ecosystems. Data on reuse costs are limited in the published lit- Current reclaimed water rates do not typically erature, although Chapter 9 provides reported capital return the full cost of treating and delivering re - and operations and maintenance costs for nine utilities claimed water to customers. Nonpotable water reuse (representing 13 facilities) that responded to a commit- customers are often required to pay for the connec- tee questionnaire. Distribution system costs can be the most sig- tion to the reclaimed water lines; therefore, some cost nificant component of costs for nonpotable reuse incentive is needed to attract customers for a product systems. Projects that minimize those costs and use that is perceived to be of lower quality based on its origin. Frequently, other revenue streams, including effluent from existing wastewater treatment plants are fees, drinking water programs, and subsidies, are used frequently cost-effective because of the minimal addi- to offset the low rates. As the need for new water tional treatment needed for most nonpotable applica- supplies in water-limited regions becomes the driving tions beyond typical wastewater disposal requirements. motivation for water reuse, reclaimed water rates are W hen large nonpotable reuse customers are located
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7 SUMMARY likely to climb so that reclaimed water resources are federal reuse regulations on the future application of used as efficiently as the potable water supplies they are water reuse to address the nation’s water needs while designed to augment. appropriately protecting public health. Modifications to the structure or implementa- tion of the Safe Drinking Water Act (SDWA) would SOCIAL, LEGAL, AND increase public confidence in the potable water sup- REGULATORY FACTORS ply and ensure the presence of appropriate controls in Water rights laws, which vary by state, affect potable reuse projects. Although there is no evidence the ability of water authorities to reuse wastewater. that the current regulatory framework fails to protect States are continuing to refine the relationship between public health when planned or de facto reuse occurs, wastewater reuse and the interests of downstream enti- federal efforts to address potential exposure to waste- ties. Regardless of how rights are defined or assigned, water-derived contaminants will become increasingly projects can proceed through the acquisition of water important as planned and de facto potable reuse ac- rights after water rights have been clarified. The right count for a larger share of potable supplies. The SDWA to use aquifers for storage can be clarified by states was designed to protect the health of consumers who through legislation or court decision. The clarifica- obtain potable water from supplies subject to many tion of these legal issues can provide a clearer path for different sources of contaminants but does not include project proponents. specific requirements for treatment or monitoring when Scientifically supportable risk-based federal source water consists mainly of municipal wastewater regulations for nonpotable water reuse would provide effluent. Presently, many potable reuse projects include uniform nationwide minimum acceptable standards a dditional controls (e.g., advanced treatment and of health protection and could facilitate broader increased monitoring) in response to concerns raised implementation of nonpotable water reuse projects. by state or local regulators or the recommendations of Existing state regulations for nonpotable reuse are expert advisory panels. Adjustment of the SDWA to developed at the state level and are not uniform across consider such requirements when planned or de facto the country. Further, no state water reuse regulations potable reuse is practiced could serve as a mechanism or guidelines for nonpotable reuse are based on rigor- for achieving a high level of reliability and public health ous risk assessment methodology that can be used to protection and nationwide consistency in the regulation determine and manage risks. The U.S. Environmental of potable reuse. In the process, public confidence in Protection Agency (EPA) has published suggested the federal regulatory process and the safety of potable guidelines for nonpotable reuse that are based, in part, reuse would be enhanced. Application of the legislative tools afforded by on a review and evaluation of existing state regulations the Clean Water Act (CWA) and SDWA to effluent- and guidelines and are not based on rigorous risk assess- impacted water supplies could improve the protec- ment methodology. Federal regulations would not only tion of public health. Increasingly, we live in a world provide a uniform minimum standard of protection, but would also increase public confidence that a water reuse where municipal effluents make up a significant part of project does not compromise public health. If nonpota- the water drawn for many water supplies, but this is not ble reuse regulations were developed at the federal level always openly and transparently recognized. Recogni- through new enabling legislation, this process should be tion of this reality necessitates increased consideration informed by extensive scientific research to address the of ways to apply both the CWA and SDWA toward wide range of potential nonpotable reuse applications improved drinking water quality and public health. For and practices, which would require resources beyond example, the CWA allows states to list public water the reach of most states. A more detailed discussion supply as a designated use of surface waters. Through of the advantages and disadvantages of federal reuse this mechanism, some states have set up requirements regulations is provided in Chapter 10. EPA should on discharge of contaminants that could adversely af- fully consider the advantages and disadvantages of fect downstream water supplies.
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8 WATER REUSE Updates to the National Pretreatment Program’s Box 11-1) hold significant potential to advance the safe, list of priority pollutants would help ensure that wa- reliable, and cost-effective reuse of municipal wastewa- ter reuse facilities and de facto reuse operations are ter where traditional sources are inadequate. Improved coordination among federal and non- protected from potentially hazardous contaminants. federal entities is important for addressing the long- The National Pretreatment Program has led to signifi- term research needs related to water reuse. Address- cant reductions in the concentrations of toxic chemicals ing the research needs identified by the committee will in wastewater and the environment. However, the list require the involvement of several federal agencies as of 129 priority pollutants presently regulated by the well as support from nongovernmental research orga- National Pretreatment Program has not been updated nizations. If the federal government decides to develop since its development more than three decades ago, national regulations for water reuse, a more robust even though the nation’s inventory of manufactured research effort will be needed to support that initiative chemicals has expanded considerably since that time, as with enhanced coordination among federal and non- has our understanding of their significance. Updates to federal entities. Such an effort would benefit from the the National Pretreatment Program’s priority pollutant leadership of a single federal agency, which could serve list can be accomplished through existing rulemaking as the primary entity for coordination of research and processes. Until this can be accomplished, EPA guid- for information dissemination. ance on priority chemicals to include in local pretreat- ment programs would assist utilities implementing * * * potable reuse. Enhanced public knowledge of water supply and Solutions to the nation’s water challenges will treatment are important to informed decision mak- require an array of approaches, involving conservation, ing. The public, decision makers, and decision influenc- supplemented as needed by alternative water supply technologies, such as reuse. Both potable and non- ers (e.g., members of the media) need access to credible potable reuse can increase the nation’s water supply, scientific and technical materials on water reuse to help although nonpotable reuse can be more expensive in ex- them evaluate proposals and frame the issues. A general isting communities that are not already equipped with investment in water knowledge, including improved dual water distribution systems. With recent advances public understanding of a region’s available water sup- in technology and treatment design, potable reuse can plies and the full costs and benefits associated with reduce the concentrations of chemical and microbial water supply alternatives, could lead to more efficient contaminants to levels comparable to or lower than processes that evaluate specific projects. Public debate those present in many drinking water supplies. Adjust- on water reuse is evolving and maturing as more proj- ments to the federal regulatory framework, including ects are implemented and records of implementation scientifically supportable risk-based regulations for are becoming available. nonpotable reuse and modifications to the structure or implementation of the SDWA for potable reuse RESEARCH NEEDS projects, would ensure a high level of public health protection for both planned and de facto reuse and The committee identified 14 water reuse research increase public confidence in water reuse. Additionally, priorities that are not currently being addressed in a improved coordination among federal and nonfederal major way. These research priorities in the areas of entities could more effectively address key research health, social, and environmental issues and perfor- needs. mance and quality assurance (detailed in Chapter 11,