Safe Drinking Water Information System
The Safe Drinking Water Information System (SDWIS) databases store information about drinking water. The federal version (SDWIS/FED) stores the information the Environmental Protection Agency (EPA) needs to monitor approximately 156,000 public water systems.
Of these, approximately 51,000 are community water systems (CWS) that serve most people in the United States (a little less than 300 million). Of these water systems, 4,221 or 8%, serve more than 246 million or 82%, of the total population. Similarly, more water systems use ground water rather than surface water as a source, but more people receive their water from a system supplied by surface water.
The state version (SDWIS/STATE) is a database designed to help states run their drinking water programs. These databases contain information submitted by states, EPA regions, and public water systems in conformance with reporting requirements established by the Safe Drinking Water Act (SDWA) and related regulations. EPA uses these data to address non-compliant systems, oversee state drinking water systems, track contaminant levels, respond to public inquiries, and prepare national reports (such as the Annual Potable Water Systems Compliance Report 2).
https://www3.epa.gov/enviro/facts/sdwis/search.html and related web pages.