Before testing water for radon, the air should be tested. If the indoor radon level is high and the homeowners use groundwater, test the water. If the radon level is low in the air, there is no need to test the water. Test results are expressed in picocuries of radon per liter of water (pCi/L). In general, 10,000 pCi/L of radon in water contributes roughly 1 pCi/L of airborne radon throughout the house. EPA currently advises consumers to take action if the total household air level is above 4 pCi/L.

For waterborne radon, a simple step to ensure reduced radon levels is to make sure the bathroom, laundry room, and kitchen are well ventilated. If the well water has only moderate levels of radon, this may adequately reduce the exposure to waterborne radon.

How is radon removed from water?

If the well has high levels of radon, it may be necessary to remove it using one of two water- treatment devices/methods, including aeration treatment or granular activated carbon (GAC) treatment.

  • Aeration treatment involves spraying water or mixing it with air, and then venting the air from the water before use.
  • Granular activated carbon (GAC) treatment filters water through carbon. Radon attaches to the carbon and leaves the water free of radon. The carbon may need special handling for disposal if it is used at a high radon level, or if it has been used for a long time.

In either method, it is important to treat the water where it enters the home (at the point of entry) so that all the water will be treated. Point-of-use devices, such as those installed on a tap or under the sink, will treat only a small portion of the water and are not entirely effective in reducing radon in the household water supply. It is important to maintain home water-treatment units properly. Failure to do so can lead to other water contamination problems. Some homeowners opt for a service contract from the installer to provide for carbon replacement and general system maintenance.


Removing radon from water by aeration takes advantage of the fact that radon is readily given off (or volatile) from water to air. Radon in water is removed by passing as much air through the water as efficiently as possible. By venting the now radon-rich air to the outdoors, aeration can remove up to 99.9% of radon from the water. Aeration is practical for central treatment of radon in water (i.e., at a water treatment plant, etc.), but it’s expensive for individual households and small public water systems. A household aeration system suitable for high-efficiency radon removal typically costs between $3,000 and $5,000. Special maintenance is required to ensure that waterborne minerals, such as iron and manganese, do not accumulate and foul the aeration system, which may reduce its radon removal efficiency.

Granular Activated Carbon (GAC) Absorption

A second method for treating radon in water is granular activated carbon (GAC) absorption. Water is filtered through granulated carbon (usually in the form of activated charcoal), and radon is attracted onto the surface of the carbon. Maximizing the carbon’s surface area and the length of filtration time is crucial to peak radon-removal efficiency. GAC absorption can remove up to 99.9% of radon from water if large amounts of carbon and long contact times are used. Typical removal efficiencies for GAC vary from 50 to 99%. GAC can be used for central treatment schemes for small systems (several hundred users or fewer), but it becomes more expensive for larger systems. GAC is also fairly cost-effective for individual residential wells. If high levels of radon are present, disposing of spent carbon filters may be difficult due to the significant amount of radioactive material present in the filter. Small carbon filters attached to kitchen faucets or under sinks are inadequate for removing radon from the home’s drinking water.


An alternative to these active mitigation systems is simple storage. Because radon is a radioactive element that decays over time (Radon-222 has a half-life of 3.8 days), radon levels in water storage tanks will decrease over time. This strategy would probably be most effective for small systems with average radon levels just a bit above the EPA’s maximum concentration level.

Another alternative for some private well owners is to connect to an existing community water system having low radon levels. Drinking bottled water alone will not completely eliminate exposure to radon in water, since this strategy does not prevent radon gas from escaping from well water into the indoor air.

In conclusion, there are straightforward procedures for the removal of radon in water. However, the air should be tested before testing water for radon. The presence of radon in the air will determine to need to test the water. If radon is present in water, either aeration treatment or granular activated carbon (GAC) treatment may be implemented to remove it. Alternatives do exist. For more information, read the How to Perform Radon Inspections Book.