Radioactivity in Drinking Water

Radioactivity in drinking water comes form two sources, naturally occurring and man made. Man made radioactivity is usually found in surface waters while naturally occurring radioactivity comes from bedrock. Public water supply companies are required to routinely monitor for radioactivity and residents served by public water should not have further concern. Water from older shallow "dug" wells are unlikely to have significant radioactivity, but water from wells drilled into bedrock may show levels of naturally occurring radioactivity.


Most homeowners in Madison do not test their wells for radioactivity and the risk of harm is considered small, but testing is available for those who are concerned. The Connecticut Department of Health (DPH) maintains a list of certified laboratories in Connecticut, which is available on the DPH website.

Radioactivity in drilled wells can come from several substances and there is not one test that can determine which one is the source. However, all sources release "alpha" particles and so the test for "Gross Alpha" particles is used to determine if further tests are indicated. There are currently no standards for radioactivity in private wells, but the standards for public water supplies can serve as a guide for private well owners. The Connecticut Department of Health Water Supply Section has recommended interpretations of the "Gross Alpha" test results, which are:

  • If 5 pCi/L or less, no further testing is needed
  • If between 5 and 15 pCi/L, test for radium 226 and radium 228
  • If above 15 pCi/L, additionally test for uranium

Health Effects

The potential health effects of radioactivity in water vary with the concentrations of the various substances found. If test results are high enough to indicate removal, there are several treatment methods available. The treatment method should be determined after the extent of the radioactivity is known.

More Information

Further information is available, but definitive answers are hard to find because there are no precise standards that government agencies or related organizations feel comfortable quoting. There is a wealth of information and further web links on the DPH website. By phone, try the EPA's Safe Drinking Water Hotline at 800-426-4791, or at the Connecticut Department of Public Health Water Supplies Section at 860-509-7333.