Radon in Water
Radon in the ground can dissolve into groundwater. When this groundwater is brought into a building, the dissolved gas is released from the water. As a rule of thumb for homes with private wells, if the well water contained 10,000 picocuries per liter (pCi/L) of radon, the amount of radon entering the home from normal water use would be 1 pCi/L of radon. Besides, there aren't any standards or recommended action levels for the amount of radon allowed in public drinking water supplies.
U.S. Environmental Protection Agency (USEPA) publications recommend testing for radon in water for all homes with private wells that have found elevated radon concentrations in air (levels greater than 4 pCi/L). However, elevated indoor radon concentrations are most often caused by radon in soil gas, not radon in household water. In fact, only in a few areas of the United States would radon from well water be expected to make a significant contribution to radon in air concentrations, and Michigan is not among those areas. Notably too, much of the health risk from radon is associated with inhalation, not ingestion, and drinking or cooking with water that contains some radon is not known to pose a significant health risk.
The Michigan Department of Environment, Great Lakes, and Energy recommends that elevated indoor radon levels be treated first as a soil gas problem, using conventional radon reduction techniques to lower those levels. Radon in water testing need not be routinely conducted and would be recommended only if the conventional techniques are not successful. Then, the homeowner may wish to test the water to determine whether it is contributing to the radon in air levels. However, it should be noted that, as of this time, there are no lists of laboratories certified to measure radon in water.
For more information on radon in water and public water standards, contact the USEPA Drinking Water Hotline (800-426-4791) or see the National Academy of Sciences, Risk Assessment of Radon in Drinking Water. Additional resource information can be found at Kansas State University's National Radon Program Services website.