Radon is a radioactive gas that occurs naturally in some rock formations and dissolves into groundwater. Unlike radon in air (which enters from soil), radon in well water is released into your home's air when you use water — showering, washing dishes, running faucets.
Radon in groundwater is most common in regions with granite and other igneous rock geology. Highest concentrations are found in:
The primary health concern from radon in well water is lung cancer from inhaled radon gas released during water use — not from drinking the water directly. The EPA estimates that radon from water contributes to approximately 168 lung cancer deaths per year in the US. Drinking radon-contaminated water also poses a small stomach cancer risk, but this is far less significant than the inhalation risk.
| Radon Level (pCi/L) | EPA Guidance | Action |
|---|---|---|
| Under 300 | Below proposed MCL | No treatment typically needed |
| 300–4,000 | Between proposed MCL and AMCL | Consider treatment or air mitigation |
| 4,000+ | Above proposed AMCL | Treatment strongly recommended |
Home radon test kits measure radon in air, not water. A separate water-specific test is required. Collect a water sample in a special radon-preserving container and ship to a certified laboratory. Contact your state health department for a list of certified radon-in-water testing labs. Cost: $25–$75.
Sprays water into a tank where radon gas escapes into the air, which is then vented outdoors. Removes 95–99% of radon. This is the most effective treatment for high radon levels. Cost: $2,000–$5,000 installed. The vented radon must exit outdoors away from windows and air intakes.
Whole-house GAC filter removes radon from water. Less effective than aeration (removes 85–95%) and the filter itself becomes radioactive over time, requiring careful disposal. Cost: $1,000–$2,000. Better suited for moderate radon levels.
If your home has high indoor radon from soil, treat the air source first. Radon in water contributes only about 1–2% of total indoor radon in most homes. A radon-in-air mitigation system (sub-slab depressurization) typically has a greater impact than water treatment on indoor radon levels.
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