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. 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 . 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. For many of these applications, there may be few technological substitutes that are as effective and reliable as desalination technologies. 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. 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. To date, the federal government primarily has supported research and development, some demonstration projects, and select full-scale facilities (often through congressionally directed spending). 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. 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. In addition to federal and private research activities, some states, such as California and Texas, also have supported desalination research. Desalination Adoption in the United States

Desalination and membrane technologies are increasingly investigated and used as an option for meeting municipal and industrial water supply and water treatment demands. As of 2005, approximately 2,000 desalination plants larger than 0.3 million gallons per day (MGD) were operating in the United States, with a total capacity of 1,600 MGD. This represents more than 2.4% of total U.S. municipal and industrial freshwater withdrawals, not including water for thermoelectric power plants. This creates uncertainty for those considering adopting desalination and membrane technologies. Environmental and human health concerns often are raised in the context of obtaining the permits required to site, construct, and operate the facility and dispose of the waste concentrate. For inland brackish desalination, significant constraints on adoption of the technologies are the uncertainties and the cost of waste concentrate disposal. Flow-through capacitive deionization shows promise for energy-efficient desalination of brackish waters.
In the United States, desalination and membrane technologies are used to augment municipal water supply, produce high-quality industrial water supplies, and reclaim contaminated supplies (including from oil and gas development). Approximately 2,000 desalination facilities larger than 0.3 million gallons per day (MGD) operate in the United States; this represents more than 2% of U.S. municipal and industrial freshwater use. At issue for Congress is what should be the federal role in supporting desalination and membrane technology research and facilities. Desalination issues before the 114th Congress may include how to focus federal research, at what level to support desalination research and projects, and how to provide a regulatory context that protects the environment and public health without disadvantaging desalination's adoption.
Desalination processes generally treat seawater or brackish water to produce a stream of freshwater, and a separate, saltier stream of water that requires disposal (often called waste concentrate). Many states (e.g., Florida, California, and Texas) and cities have investigated the feasibility of large-scale municipal desalination. Coastal communities look to seawater or estuarine water, while interior communities look to brackish aquifers. The most common desalination technology in the United States is reverse osmosis, which uses permeable membranes to separate freshwater from saline waters. Membrane technologies are also effective for other water treatment applications. Many communities and industries use membranes to remove contaminants from drinking water, treat contaminated water for disposal, and reuse industrial wastewater. For some applications, there are few competitive technological substitutes.
Wider adoption of desalination is constrained by financial, environmental, and regulatory issues. Although desalination costs have dropped in recent decades, significant further decline may not happen with existing technologies. Electricity expenses represent one-third to one-half of the operating cost of many desalination technologies. The energy intensity of some technologies raises concerns about greenhouse gas emissions and the usefulness of these technologies for climate change adaptation. Concerns also remain about the technologies' environmental impacts, such as saline waste concentrate management and disposal and the effect of surface water intake facilities on aquatic organisms. Construction of desalination facilities, like many other types of projects, often requires a significant number of local, state, and federal approvals and permits. Emerging technologies (e.g., forward osmosis, capacitive deionization, and chlorine resistant membranes) show promise for reducing desalination costs. Research to support emerging technologies and to reduce desalination's environmental and human health impacts is particularly relevant to future adoptions of desalination and membrane technologies.
The federal government generally has been involved primarily in desalination research and development (including for military applications), some demonstration projects, and select full-scale facilities. For the most part, local governments, sometimes with state-level involvement, are responsible for planning, testing, building, and operating desalination facilities. Some states, universities, and private entities also undertake and support desalination research. While interest in desalination persists among some Members, especially in response to drought concerns, efforts to maintain or expand federal activities and investment are challenged by the domestic fiscal climate and differing views on federal roles and priorities.