According to EPA, about 52,000 community water systems use energy to treat and deliver drinking water to over 290 million Americans. In a typical drinking water treatment plant, large debris and contaminants are physically removed from the raw water using screens (see fig. 2). Next, dirt and other particles suspended in the water are removed through the addition of alum and other chemicals during the processes of coagulation and sedimentation. After these particles have separated out, the water passes through filters made of layers of materials such as sand, gravel, and charcoal to remove even smaller particles. At this point, the water is stored in a closed tank or reservoir, allowing time for disinfection which kills many disease-carrying organisms. The treated water is pressurized for distribution to consumers. The distribution infrastructure consists of pumps, pipes, tanks, valves, hydrants, and meters that support delivery of water to the customer and control flow and water pressure. Once water is delivered, residential consumers use it for a variety of purposes, including for drinking; bathing; preparing food; washing clothes and dishes; and flushing toilets, which can represent the single largest use of water inside the home. Energy is needed to accomplish many of these activities. For example, energy is used in homes to filter and soften water and to heat it for use in certain appliances, which accounts for 12.5 percent of a typical household’s energy use, according to DOE. In addition to residential water users, commercial, industrial, and institutional customers use energy for water-related purposes. For example, energy is used to produce hot water and steam for heating buildings, to cool water for air conditioning buildings, and to generate hot water needed to manufacture or process materials, such as food and paper. After water is used by customers, energy is needed to collect and treat wastewater, and to discharge effluent into a water body. Wastewater service is provided to more than 220 million Americans by about 15,000 municipal wastewater treatment facilities. During a typical wastewater treatment process, solid materials, such as sand and grit, organic matter from sewage, and other pollutants, are removed before the treated effluent is discharged to surface waters. Systems for collecting, treating, and disposing of municipal wastewater vary widely in terms of the equipment and processes used, and wastewater may go through as many as three treatment stages—primary, secondary, and advanced treatment—before water is discharged (see fig. 3). Preliminary and primary treatment. As wastewater enters a treatment facility, it is screened to remove large debris and then passes through a grit removal system to separate out smaller particulate matter. After preliminary screening and settling, primary treatment removes solids from the wastewater through sedimentation. Solids removed during the treatment process may be further treated and used for other applications, such as fertilizer; incinerated; or disposed of in landfills. Secondary treatment. After primary treatment, the wastewater undergoes secondary treatment to remove organic matter and suspended solids through physical and biological treatment processes. Activated sludge is the most commonly used biological treatment process in secondary treatment of wastewater. This process relies on micro-organisms to break down organic matter in the wastewater. More specifically, aeration— whereby blowers or diffusers inject oxygen into the wastewater—enables the micro-organisms to digest the organic matter. After being pumped into an aeration tank to allow time for digestion, the wastewater is next pumped to a secondary settling tank for removal of digested material. After secondary settling, the effluent either is disinfected and discharged into a water body, or it undergoes advanced treatment. Advanced treatment. Most wastewater goes through at least secondary treatment. However, before treated wastewater can be released in some receiving waters, it may need to be further treated to reduce its effect on water quality and aquatic life after discharge. Over 30 percent of wastewater treatment facilities provide this kind of advanced treatment, which can remove additional contaminants. Two key pieces of federal legislation—the Safe Drinking Water Act and the Clean Water Act—govern the treatment of drinking water and wastewater. Each municipality or water utility generally may choose amongst technologies for achieving a given standard. Under the Safe Drinking Water Act, EPA has established National Primary Drinking Water Standards for specified contaminants and has the authority to regulate additional contaminants that the agency determines may have adverse health effects, are likely to be present in public water supplies, and for which regulation presents a meaningful opportunity for health risk reduction. EPA’s regulations establish a limit, or maximum contaminant level, for specific contaminants and require water systems to test the water periodically to determine if the quality is acceptable. EPA has regulations in place for 89 contaminants, including disinfectants, byproducts of disinfectants, and microbial contaminants, but has not issued a regulation under the Safe Drinking Water Act for a new contaminant since 2000. The Clean Water Act governs the discharge of pollutants into the waters of the United States, including the treatment of wastewater discharged from publicly owned treatment facilities. Specifically, industrial and municipal wastewater treatment facilities must comply with the National Pollutant Discharge Elimination System (NPDES) permits that control pollutants that facilities may discharge into the nation’s surface waters. The act requires that municipal wastewater treatment plants provide a minimum of secondary treatment prior to discharge. In some cases, modification of secondary treatment requirements may occur, however, for discharges into marine waters under certain conditions. For example, the discharge may not interfere with that water quality which assures protection of public water supplies and the protection and propagation of a balanced, indigenous population of shellfish, fish, and wildlife and allows recreational activities on the water. In 2000, Congress amended the Clean Water Act to require permits for discharges from combined sewers— sewers that transport both wastewater and stormwater to the municipal wastewater treatment plant—to conform with EPA’s Combined Sewer Overflow Control Policy, which requires systems to demonstrate implementation of certain minimum pollution control practices. Combined sewers may overflow when there is heavy precipitation or snowmelt, resulting in the discharge of raw sewage and other pollutants into receiving water bodies. Comprehensive data about the energy needed for each stage of the urban water lifecycle are limited, and few nationwide studies have been conducted on the amount of energy used to provide drinking water and wastewater treatment services to urban users. However, specialists with whom we spoke emphasized that the energy demands of the urban water lifecycle vary by location; therefore, consideration of location-specific and other factors is key to assessing the energy needs of the urban water lifecycle. These factors include the source and quality of the water, the topography of the area over which water is conveyed and the distance of conveyance, and the level and type of treatment required. Providing a reliable and comprehensive estimate of the total energy requirements for moving, treating, and using water in urban areas is difficult, in part, because comprehensive data on the energy demands of the urban water lifecycle are limited and few nationwide studies have been conducted to quantify the amount of energy used throughout the lifecycle. Two studies most often cited by the specialists we spoke with were conducted by the Electric Power Research Institute (EPRI) on the energy needs of the urban water lifecycle. These studies concluded that 3 to 4 percent of the nation’s electricity is used to move and treat drinking water and wastewater. While some specialists noted that these studies provide reasonable estimates of the energy demands of the urban water lifecycle, other specialists raised a number of concerns with the studies. In particular, according to several specialists, the EPRI studies are outdated. The first study dates back to 1996, and the more recent study was conducted in 2002 but relied on projections of future water use based on statistics compiled in 2000. Some specialists also told us these studies do not reflect the treatment processes that have been implemented over the last decade, which have increased the amount of energy needed to treat water. In addition, the studies do not include all stages of the urban water lifecycle—specifically, they omit energy used by customers. Because they exclude end use, the EPRI studies underestimate the energy demands of the entire lifecycle because customer end use, including use by residential customers, can be the most energy-intensive stage of the entire lifecycle, according to some specialists we spoke with and studies that we reviewed. Some specialists also added that the studies underestimate total energy demands because they include only electricity, excluding other fuel types that can be used throughout the lifecycle. For example, the studies do not assess the use of natural gas, which can be a primary energy source at wastewater treatment plants for certain processes. Furthermore, some specialists explained that the studies do not use actual measured data, relying instead on previously published estimates of energy used for portions of the water lifecycle. Furthermore, some specialists noted that there are limited data on the amount of energy associated with customer water use. Federal agencies like DOE’s Energy Information Administration collect some data on energy used to heat water in residences and in the commercial sector, but these data are reported on a national level and do not allow for analysis at the local level. In addition, data needed to get a full picture of the energy needs for water in an urban setting may not be readily available at the local level. Specifically, water utilities may not have detailed data on their facilities’ energy use, may not have conducted audits to understand how their facilities use energy, or may be reluctant to share data, according to specialists we spoke with. Many of the specialists told us that efforts to assess the energy needs of the urban water lifecycle on a national scale can be difficult, and the majority of the specialists we spoke with emphasized that to obtain a more accurate picture, one needs to consider location-specific and other factors that influence energy use. The specialists identified the following as key factors that must be considered for such an assessment. Type of water source. Drinking water systems that rely on surface water are often designed to take advantage of gravity and use little to no energy to extract water from the source and convey it to the treatment facility.