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 even greater if the water can again be captured and reused. Inland effluent discharges may also be available for water reuse, although extensive reuse has the potential to affect the water supply of downstream users and ecosystems in water-limited settings. Water reuse alone cannot address all of the nation’s water supply challenges, and the potential contributions of water reuse will vary by region. However, water reuse could offer significant untapped water supplies, particularly in coastal areas facing water shortages.
Water reuse is a common practice in the United States. Numerous approaches are available for reusing wastewater effluent to provide water for industry, irrigation, and potable supply, among other applications, although limited estimates of water reuse suggest that it accounts for a small part (<1 percent) of U.S. water use. Water reclamation for nonpotable applications is well established, with system designs and treatment technologies that are generally accepted by communities, practitioners, and regulatory authorities. The use of reclaimed water to augment potable water supplies has significant potential for helping to meet future needs, but planned potable water reuse only accounts for a small fraction of the volume of water currently being reused. However, potable reuse becomes more significant to the nation’s current water supply portfolio if de facto (or unplanned) water reuse2 is included. The de facto reuse of wastewater effluent as a water supply is common in many of the nation’s water systems, with
2 De facto reuse is defined by the committee as a drinking water supply that contains a significant fraction of wastewater effluent, typically from upstream wastewater discharges, although the water supply has not been permitted as a water reuse project. There is no specific cutoff for how much effluent in a water source is considered de facto reuse, because water quality is affected by the extent of instream contaminant attenuation processes and travel time. However, water supplies where effluent accounts for more than a few percent of the overall flow are usually considered to be undergoing de facto reuse. For a detailed discussion of the extent of effluent contributions to water supplies, see Chapter 2.