Although soil gas is the primary source of radon in homes, radon is water-soluble and can enter the water supply from surrounding bedrock and contribute to indoor radon levels. Homeowners concerned that radon may be entering the home through the water supply should first conduct an air sampling and treat air problems according to standard recommendations. If indoor radon levels cannot be successfully mitigated subsequent water sampling may confirm a radon-in-water problem. To date, epidemiological studies have not found an association between radon in drinking water and cancer of the digestive and other systems. These studies concluded that the highest radon-in-water concentrations generally occur in portions of the Appalachian Mountains, Rocky Mountains, and Basin and Range. The studies also concluded:
- Private well sources and small public water supplies tend to be higher in radon than large public water supplies.
- Radon concentration in the water tends to be high in areas where aquifers are comprised of uranium bearing granite, metamorphic rocks, or fault zones (as found in the mountain states).
- Large public water supplies tend to be lower in radon because they use high-capacity sand and gravel aquifers, which generally comprise low-uranium rocks and sediments.
- Private water supplies were higher in radon than public water supplies by factors of 3 to 20.
- Rhode Island, Florida, Maine, South Dakota, Montana, and Georgia were the states with the highest radon in private well water.
- The New England states overall had the highest radon concentrations in water from all sources.
EPA guidelines suggest that it takes approximately 10,000 pCi/L of radon in water to give an airborne concentration of 1pCi/L. Most of the risk from radon in water comes from radon released into the air when water is used for showering and other household purposes.
The ability for radon to transfer from water to air relies on 4 principles:
- The waterborne radon level.
- The amount of water used.
- The type of water activity (i.e. shower vs. faucet)
- The air and water temperatures.
Measuring and Mitigating Radon in Water
- Very difficult to measure & mitigate.
- Expensive to mitigate.
- First line of defense:
- Test and mitigate indoor radon levels in the air.
- If there is a problem with indoor air levels that can’t be mitigated, then test the water and pursue mitigation options.
- Some experts have said it’s more economical to simply ventilate the area being used when steam is generated than it is to mitigate radon in water!