The Environmental Protection Agency (EPA) provides a range of resources which address the health effects of contaminants in drinking water. Their Drinking Water Contaminants page provides a useful background on the sources and effects of drinking water contaminants for the following contaminant types:

• Physical
• Chemical
• Biological
• Radiological
   

Learn More:

• National Primary Drinking Water Regulations (Tables) Environmental Protection Agency
  Tables of regulated contaminants and their effects on human health

• Water On Tap: What You Need To Know (Report) Environmental Protection Agency
  Detailed report for consumers that answers a selection of questions about drinking water

• Water-Quality Data For the Nation (Database) U.S. Geological Survey
  Database of current and historical information on local water quality across the U.S.

• Health Effects of Drinking Water Contaminants (Factsheet) Clemson University Cooperative Extension Service
  Information on the effects, identification and treatment of drinking water contaminants