Interest in using desalination technologies to treat seawater, brackish water, wastewaters, and contaminated sources has increased globally and in the United States, as costs have fallen and pressure to develop drought-proof water supplies has grown. Adoption of desalination, however, remains constrained by financial, environmental, regulatory, and social factors. At issue is the role Congress establishes for the federal government in desalination, particularly in desalination research and development and the federal regulatory environment for desalination projects. Also of congressional interest is what role desalination may play in meeting water demands. Desalination processes generally treat saline or impaired waters to produce a stream of freshwater, and a separate, saltier stream often called waste concentrate or brine . The availability and regulation of disposal options for waste concentrate can limit adoption in some locations; this is a particular challenge for large-scale inland facilities. For seawater desalination, the impacts of intake facilities on marine life also often are raised as concerns. Desalination's attractions are that it can create a new source of freshwater from otherwise unusable waters, and that this source may be more dependable and drought-proof than freshwater sources that rely on annual or multi-year precipitation, runoff, and recharge rates. Another significant application of desalination technologies is for treatment of contaminated waters or industrial water or municipal wastewater. Some communities and industries use desalination technologies to produce drinking water that meets federal standards, to treat contaminated water supplies to meet disposal requirements, or to reuse industrial wastewater. Many of the technologies developed for desalination also can produce high-quality industrial process water. For many of these applications, there may be few technological substitutes that are as effective and reliable as desalination technologies. There are multiple desalination methods. Two common categories of desalination technologies—thermal (e.g., distillation) and membrane (e.g., reverse osmosis)—are the most common, with reverse osmosis technologies dominating in the United States. For more information on traditional and emerging technologies, see Appendix A . Desalination treatment costs have dropped in recent decades, making the technology more competitive with other water supply augmentation and treatment options. Electricity expenses vary from one-third to one-half of the cost of operating desalination facilities. A rise in electricity prices could reverse the declining trend in desalination costs; similarly, drops in electricity costs improve desalination's competitiveness. Costs and cost uncertainties remain among the more significant challenges to implementing large-scale desalination facilities, especially seawater desalination plants. Desalination's energy intensity also raises concerns about the greenhouse gas emissions emitted and desalination's usefulness as part of a climate change adaptation strategy. Substantial uncertainty also remains about the environmental impacts of large-scale desalination facilities. Social acceptance and regulatory processes also affect the technologies' adoption and perceived risks. Research and additional full-scale facilities may resolve uncertainties, alleviate concerns, and contribute to cost reductions and options for mitigating environmental impacts. To date, the federal government primarily has supported research and development, some demonstration projects, and select full-scale facilities (often through congressionally directed spending). The federal government also may support construction of municipal desalination facilities through loans or other credit assistance provided through programs of the U.S. Environmental Protection Agency (EPA). For most municipal desalination facilities, local governments or public water utilities (often with state-level involvement and federal construction loans) have been responsible for planning, testing, building, and operating desalination facilities, similar to their responsibility for treating freshwater drinking water supplies. During recent Congresses, legislative proposals have identified a range of different potential federal roles in desalination. Desalination issues before the 114 th Congress may include how to focus federal research to produce results that provide public benefits, at what level to support desalination research and projects, and how to provide a regulatory context that protects the environment and public health without unnecessarily disadvantaging these technologies. The 113 th Congress authorized a new federal credit assistance program, the Water Infrastructure Finance and Innovation Act (WIFIA, 33 U.S.C. §3901), as part of P.L. 113-121 . The portion of the program administered by EPA may be used in financing a range of water projects, including desalination projects. The Water Desalination Act of 1996, as amended (42 U.S.C. §10301), authorized the main desalination research and demonstration outreach program of the Department of the Interior, which is carried out by the Bureau of Reclamation. The 112 th Congress extended through FY2013 its annual authorization of appropriations at $3 million. Bills in the 113 th Congress proposed another extension, but the 113 th Congress did not extend the authorization of appropriations. Although an extension was not enacted, the 113 th Congress provided appropriations for these desalination research and demonstration activities (e.g., $1.75 million for FY2015) and for operation and maintenance of the Department of the Interior's operation of the Brackish Groundwater National Desalination Research Facility ($1.15 million for FY2015). Several reports since 2000 have aimed to inform the path forward for U.S. desalination research. The first was the 2003 Desalination and Water Purification Technology Roadmap produced by the Bureau of Reclamation and Sandia National Laboratories at the request of Congress. The National Research Council then reviewed the roadmap in a 2004 report, Review of the Desalination and Water Purification Technology Roadmap , which called for a strategic national research agenda. To this end, the National Research Council (NRC) convened a Committee on Advancing Desalination Technology. That NRC committee published its own assessment in 2008, Desalination: A National Perspective . The NRC concluded that research should focus on reducing desalination costs and that substantial further cost savings were unlikely to be achieved through incremental advances in the commonly used technologies, like reverse osmosis. Consequently, the report recommended that federal desalination research funding be targeted at long-term, high-risk research not likely to be attempted by the private sector that could significantly reduce desalination costs. It also recommended a line of research on minimizing or mitigating the environmental impacts of desalination. The NRC specifically identified for federal investment research that had potential for widespread benefit and that the private sector had little willingness to perform. (See "National Research Council 2008 Desalination Research Recommendations" box for more details.) In 2010, the Water Research Foundation, WateReuse Foundation, and Sandia National Laboratories published a report on how to implement the 2003 roadmap. The report identified research agendas for a range of topics—membrane and alternative technologies, concentrate management, and institutional issues such as energy cost reduction and regulatory compliance. No single federal agency has responsibility for all federal desalination and membrane research; instead numerous agencies and departments are involved in research based on their specific missions. In FY2005, FY2006, and FY2007, federal desalination research totaled $24 million, $24 million, and $10 million, respectively. (These are the most recent comprehensive data on federal desalination funding.) The Bureau of Reclamation was responsible for half or less of that spending at $12 million, $11 million, and $4 million, respectively. Other agencies and departments with spending on desalination research included the Army, National Science Foundation, Office of Naval Research, U.S. Geological Survey, and four of the Department of Energy's National Laboratories. Sandia National Laboratory has had the largest role among the national laboratories. In FY2005 and FY2006, much of the federal desalination research was congressionally directed to specific sites and activities. The level of funding fell after FY2006, when the appropriations process began to include less congressionally directed spending. The optimal level and type of federal support for desalination research is inherently a public policy question shaped by factors such as fiscal priorities and views on the appropriate role of the federal government in research, industry development, and water supply. Federal support for desalination research raises questions, such as what should be the respective roles of federal agencies, academic institutions, and the private sector in conducting research and commercializing the results, and should federal research be focused on basic research or promoting the use of available technologies? In addition to federal and private research activities, some states, such as California and Texas, also have supported desalination research. In 2008, the National Research Council recommended a federal desalination research level of roughly $25 million, but recommended that the research be targeted strategically, including being directed at the research activities described above. The NRC drew the following conclusion: There is no integrated and strategic direction to the federal desalination research and development efforts. Continuation of a federal program of research dominated by congressional earmarks and beset by competition between funding for research and funding for construction will not serve the nation well and will require the expenditure of more funds than necessary to achieve specified goals. No recent authoritative estimate of all federal desalination spending is available. Data for Reclamation indicate a reduction in federal desalination spending. Reclamation's desalination funding has declined from $11 million in FY2006 to between $2 million and $4 million in recent years, with FY2015 funding at $3 million. While some traditional avenues for federal desalination research may be receiving less support, new avenues of support may be opening. Two of these are the Advanced Research Projects Agency-Energy (ARPA-E) and the National Science Foundation's Urban Water Engineering Research Center, which was initiated in 2011. Desalination and membrane technologies are increasingly investigated and used as an option for meeting municipal and industrial water supply and water treatment demands. The nation's installed desalination capacity has increased in recent years, reflecting the technology's growing competitiveness and applications and increasing demands for reliable freshwater supplies.