The USGS National Water Quality Program investigates the quality of water pumped from public-supply wells across the United States. These wells are the source of drinking water and water for other household needs for more than one-third of the U.S. population. There are about 140,000 public water systems that use groundwater as their source. Although the quality of finished drinking water from these public water systems is regulated by the EPA under the Safe Drinking Water Act (SDWA), long-term protection and management of groundwater, a vital source of drinking water, requires an understanding of the occurrence of contaminants in untreated source water. This web page provides an overview of USGS's research about public supply wells. It includes related research, publications, maps, and a collection of data and tools (Introduction).