Radon in water is only an issue with well water, not municipal water. Because well water comes from the ground, it may contain contaminants like radon and other radionuclides like radium and uranium.
Is drinking well water that contains radon harmful?
Not a lot of research has been conducted about the safety of drinking water that contains radon. Scientists believe consumption may potentially lead to stomach and intestinal cancer, but the statistics are very low.
The EPA estimates that radon in drinking water causes approximately 168 cancer deaths per year in the United States. The majority of these deaths are attributed to breathing in radon that has gassed out of the well water (as opposed to drinking it).
Radon in water is primarily a concern in relation to how much radon off-gases into the air while washing clothes, dishes, bathing, etc. (and contributes to the indoor radon levels). The radon levels in the water have to be very high to measurably contribute to the radon in air - it’s estimated that every 10,000 pCi/L in the water contributes to 1 pCi/L in the indoor air. The EPA also estimates that around 90% of radon in the home comes from beneath the foundation - the remainder may come from building materials (concrete, granite, etc.) and water.
What's the best way to protect myself and my family?
If you have a private well, the best thing to do is conduct a radon-in-air test every 2-5 years, or whenever significant changes are made to the home. Assuming the water is in use during the testing period for bathing, cleaning, etc., the air test will include radon that's coming from the ground beneath the home as well as what's off-gassing from the water. If your indoor air radon levels are low, further action is likely not warranted (other than routine re-testing).
If the results of your radon-in-air test are elevated (or higher than you'd like), the next step would be to determine the source - the ground or the water (or both). A radon-in-water test can be conducted to determine the extent of radon contamination in the well water. If the radon-in-water levels are relatively low (less than 10,000 pCi/L in water), the water is likely not the source.
How can I test my well water for radon?
Contaminants in well water can change over time, so private wells should be tested for all contaminants regularly (every 2-5 years). Be sure your routine well inspections include testing for radon - it may be an "add-on" service through your well inspection company.
If you're having a comprehensive inspection performed by a well inspection company, it may be easiest to ask them to also test the water for radon.
If you want to test for radon only, the easiest way is to purchase a test kit online. You can purchase one through Accustar Labs for about $35. Your kit will include detailed instructions, but testing basically involves shipping a vial of non-aerated tap water to a laboratory for analysis.
Where can I find more information about radon in well water?
Wake County, NC has had a recent public service campaign to inform local homeowners about the importance of testing well water for radon and other radionuclides, and they have a very helpful website. If you live in Wake County, you can search your address to find out whether your home falls within their recommended testing area.
You can also visit the EPA's website on radon in well water for national information.