The primary source of radon in homes is from the underlying soil and bedrock. However, an additional source could be the water supply, particularly if the house is served by a private well or a small community water system.
If your home or the home you are considering buying has been found to have radon in air concentrations of 4 picocuries per liter (pCi/L), or greater, (EPA 'Action Level') you may want to consider having the water tested if the house is served by a private well or a community well, e.g., underground sources. Many public water supplies use surface water which tends to have lower radon levels. If you are concerned about the public water supply, call your public water supplier. Testing for radon in water is not very expensive ($25 - $50) and is fairly easy to do.
Radon in water can be effectively reduced using one of two methods: aeration treatment or granular activated charcoal.
Aeration involves spraying the water or mixing it with air and then venting the radon. Granular activated charcoal systems filter the water through a charcoal bed. The radon is retained in the charcoal and the water leaves the charcoal tank relatively free of radon. The charcoal needs to be replaced on a regular basis.
In both of these treatment methods, it is important to treat the water where it enters the home. Trying to treat the water at the kitchen sink, for instance, would not be effective in reducing the amount of radon that enters the home. It is important to properly maintain home water treatment systems according to manufacturer's recommendations since failure to do so can lead to other water contamination problems. Aeration systems cost approximately $3,000 - $4,000. Charcoal systems cost approximately $1,000 - $1,500.
If you want to estimate how much of the radon in the air is caused by radon in the water, use the following rule of thumb. For every 10,000 pCi/L of radon in the water, 1 pCi/L would be emitted into the air. For example, if there is 40,000 pCi/L in the water, this will contribute about 4 pCi/L to the air.
The U.S. Environmental Protection Agency (EPA) is developing a regulation to limit the amount of radon in public drinking water supplies. EPA does not currently regulate radon in drinking water. The proposed EPA regulation will address radon in public water supplies (systems serving 25 or more individuals, or with 15 or more service connections). It is expected that the EPA will adopt a Maximum Contaminant Level (MCL) for radon that will affect both public community water supplies (CWS) and non-transient non-community water supplies (NT/NCWS) such as schools and hospitals, which rely on ground water as their primary water source.
Private wells are not regulated under the federal Safe Drinking Water Act. When promulgated, the MCL for radon in drinking water may provide useful guidance for individual homeowners, and will likely be of interest to home buyers and sellers. The Safe Drinking Water Hotline (1 (800) 426-4791) can provide general information on radon in water, and information on how to find a testing laboratory. The National Radon Hotline at 1 (800) SOS-RADON (1 (800) 767-7236) can provide guidance on testing indoor air for radon.
For more information, please contact the Safe Drinking Water Hotline at 1 (800) 426-4791, or EPA's homepage for drinking water.
For further information on radon in water, contact the state radon office (1 (800) 237-2366). Information also can be found in the following EPA publications: