Limits for Contaminants in Drinking Water and Ground Water

Below you will find a comprehensive database of contaminants commonly found in drinking water and groundwater. The list includes contaminants which the EPA classifies as “Primary Contaminants”. Primary Contaminants are regulated and have strict mandatory/enforceable limits. The list also includes EPA designated “Secondary Contaminants”. These are contaminants which the EPA has set limit guidelines for the public, but has not set mandatory/enforceable limits. Secondary Contaminant limits have been established by the EPA in order to help protect the public against the consumption of drinking water contaminants that pose a health risk to humans. The list also includes some other contaminants that may not be listed in the EPA Primary or Secondary Contaminant lists.

The information on this page primarily comes from the EPA (see the REFERENCES/SOURCES tab in the database below), however, other reputable sources are also included. This page is updated on an on-going basis as EPA regulations change and as other pertinent water quality information becomes available. This page is NOT meant to be used as a source/reference for enforcing any regulations. For questions regarding water regulations, please refer to the EPA website. If you are concerned about the safety of your water supply, please contact your local municipality or the EPA.


  • MCL = Maximum Contaminat Level
  • mg/L = ppm (for example, 1 mg/L = 1 ppm)
  • N/A = Not Applicable