The best way to learn about your local drinking water quality is to read the annual drinking water quality report/consumer confidence report that water suppliers now send out by July 1 of each year. The reports are often sent out with water bills, but they may be sent separately. The reports tell where drinking water comes from, what contaminants are in it, and at what levels.
The U.S. Environmental Protection Agency offers information about local drinking water systems through their Office of Ground Water and Drinking Water. Many water suppliers are now posting their water-quality monitoring results on the Web, and many of these results can be accessed from the EPA site Drinking Water Data and Reports.
The National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey has completed a study that assesses water-quality conditions for about 2,100 domestic wells across the United States.
Learn more: USGS Drinking Water and Source Water Research