Radon in well water: levels, risks and aeration
There is no federal limit for radon in private well water. Maine and several other states advise treatment above 4,000 pCi/L, the same as EPA's proposed alternative level. Most of the risk comes from radon released into the air when you use water.
- US
- No federal limit. Maine uses 4,000 pCi/L, matching EPA's proposed alternative level.
- Ontario
- No limit for water. Health Canada focuses on radon in indoor air.
What it is
Radon is a radioactive gas from uranium in bedrock, common in granite areas such as New England. It escapes from water into the air when you shower, do laundry or run the dishwasher, so radon in water adds to radon in the air you breathe.
What your number means
- Within guidelineBelow 4,000 pCi/L
Under the guideline used by Maine. Test your indoor air too, since that is the bigger source for most homes.
- Above guidelineAbove 4,000 pCi/L
Ask about an aeration system and test your indoor air.
- HighAbove 10,000 pCi/L
Treat it. Aeration systems remove most radon from water.
What to do
- Test your indoor air for radon. Air is usually the larger exposure.
- Above 4,000 pCi/L, ask about a point of entry aeration system, which removes most radon from water.
- Carbon filters also remove radon but can build up radioactivity, so they are usually only used for lower levels.
- Retest after treatment to confirm it works.
How often to test
Once, and again every few years or after any change to the well. Use a lab that follows radon sampling steps, since radon escapes quickly from a poorly collected sample.
Common questions
Is radon in water dangerous to drink?
Drinking it adds a small risk of stomach cancer, but most of the risk is breathing radon released from water into the air.
What is pCi/L?
Picocuries per liter, a unit of radioactivity. Canadian labs may report Bq/L. One Bq/L is about 27 pCi/L.
Sources: Maine CDC: radon in water guideline; EPA radionuclides rule. Limits checked November 2026.