An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »


Where can I find more information about radionuclides in drinking water?

Under the Safe Drinking Water Act (SDWA), the EPA sets legal limits on the levels of certain radionuclides in drinking water. Under SDWA, the Agency established a dose-based Maximum Contaminant Level (MCL) for beta particle and photon (gamma) radioactivity of 4 mrem/yr. The MCL is based on lifetime exposure criteria, which assume 70 years of continued exposure to contaminants in drinking water.

Additionally, the EPA has developed a non-regulatory drinking water protective action guide (PAG) that can protect the public in the event of a radiological incident that affects drinking water supplies. The purpose of the protective action guidance for drinking water is to restrict the use of contaminated water for drinking and to provide recommendations for local communities on providing alternative sources of drinking water. The drinking water PAGs apply during the intermediate phase of an incident, which may last for weeks to months but not longer than one year. This guidance does not in any way affect public water systems' compliance obligations under applicable National Primary Drinking Water Regulations promulgated under the Safe Drinking Water Act (SDWA).

For more information, visit Safe Drinking Water Act or Protective Action Guides (PAGs).

Return to Frequent Questions About RadNet.