Perchlorate is the explosive component of solid rocket fuel, fireworks, road flares, and other products. Used mainly by the Department of Defense (DOD) and related industries, perchlorate occurs naturally and is present in some organic fertilizer. This soluble, persistent compound has been detected in sources of drinking water for more than 11 million people. It also has been found in milk, fruits, and vegetables. Concern over the potential health risks of perchlorate exposure has increased, and some states and Members of Congress have urged the Environmental Protection Agency (EPA) to set a drinking water standard for perchlorate. The EPA has not determined whether to regulate perchlorate and has cited the need for more research on health effects, water treatment techniques, and occurrence. Related issues have involved environmental cleanup and water treatment costs, which will be driven by federal and state standards. Interagency disagreements over the risks of perchlorate exposure led several federal agencies to ask the National Research Council (NRC) to evaluate perchlorate s health effects and EPA s risk analyses. In 2005, the NRC issued its report, and the EPA adopted the NRC's recommended reference dose (i.e., the expected safe dose) for perchlorate exposure. However, new studies raise more concerns about potential health risks of low-level exposures, particularly for infants. Perchlorate bills in the 110th Congress include S. 150 and H.R. 1747, which direct the EPA to set a standard. This report reviews perchlorate water contamination issues and developments.