RadonRadonA radioactive gas that dissolves into groundwater from natural uranium decay in rock. Released into indoor air during showering and other water use.EPA proposed MCL: 300 pCi/L (not yet finalized)Learn more → (a radioactive gas from natural uranium decay) is invisible, odorless, and tasteless. You cannot detect it without a test.
When radon is dissolved in well water, it escapes into your indoor air every time you shower, wash dishes, or do laundry. Radon is the #1 cause of lung cancer among non-smokers[5].
Quick Answer
The EPA proposed MCLMCL (Maximum Contaminant Level)The highest level of a contaminant allowed in public drinking water, set by the EPA. Private wells are not regulated by MCLs, but they serve as the best available safety benchmarks.Learn more → (maximum contaminant level) for radon in water is 300 pCi/L. It has not been finalized[2]. An aeration system ($3,000–$5,000) is the most effective treatment. A granular activated carbon (GAC) tank ($1,000–$2,500) works for moderate levels. Both require professional installation.
What Is Radon and Why Is It in Your Well?
Radon forms when uraniumUraniumA radioactive element found naturally in certain rock formations. Long-term exposure through drinking water can damage kidneys.EPA MCL: 30 µg/L (ppb)Learn more → (a radioactive element in rock) decays naturally underground. The gas dissolves into groundwater as it flows through rock and soil[4].
Think of it like carbonation in soda. The gas is dissolved under pressure underground. When water reaches your tap, the pressure drops and radon escapes into the air — just like fizz from an opened bottle.
Geology determines your risk. Radon is highest in areas with:
- Granite bedrock: The most common radon source. New England is heavily affected.
- Shale and limestone: Common across Appalachian states.
- Phosphate-rich deposits: Parts of Florida and the Southeast.
- Glacial deposits: Upper Midwest[4].
Have your water test results handy? Get a treatment plan based on your exact numbers.
Analyze My Water TestHealth Risks of Radon in Water
Radon causes lung cancer. It is responsible for about 21,000 lung cancer deaths per year in the U.S.[10]. Most of that risk comes from radon in indoor air (from soil). But radon in water adds to your total exposure.
The EPA estimates radon in drinking water causes about 168 cancer deaths per year[3]. The risk comes from two pathways:
- Inhalation (89% of risk): Radon escapes from water into indoor air during showers, dishwashing, and laundry. You breathe it in.
- Ingestion (11% of risk): Drinking water with dissolved radon delivers a small dose to your stomach.
Rule of thumb: 10,000 pCi/L of radon in water adds roughly 1 pCi/L to your indoor air[1]. The EPA action level for indoor air is 4 pCi/L.
What Your Radon Level Means
| Level (pCi/L) | Status | Context | What to Do |
|---|---|---|---|
| 0–300 | Low Risk | Below EPA proposed MCL. | No treatment needed. Retest in 5 years. |
| 300–4,000 | Elevated | Exceeds proposed MCL. Adds to indoor air exposure. | Consider GAC treatment. Also test indoor air. |
| 4,000–10,000 | Priority | Significantly elevated. Meaningful cancer risk addition. | Install aeration or GAC system. Test indoor air. |
| 10,000+ | Urgent | Very high. Adds ~1+ pCi/L to indoor air. | Install aeration system. Treat immediately. |
Context matters. If your indoor air radon is already near 4 pCi/L, even moderate levels in water make the total worse[5]. Test both air and water for the full picture.
How to Test for Radon in Water
Standard well water tests do not include radon. You must request a radon-specific water test.
Cost: $40–$150 at a certified lab. The sample must be collected carefully. Radon escapes from water quickly — like fizz leaving soda[8].
How to collect: Fill the sample vial slowly. No splashing. Cap it immediately. Send it to the lab within 24 hours. Follow the lab's instructions exactly.
Also test your indoor air. A home radon air test kit costs $15–$30. This tells you your total radon exposure from all sources (soil + water).
2 Ways to Remove Radon from Well Water
Aeration System ($3,000–$5,000)
An aeration system bubbles air through your water. Radon transfers from the water into the air. A fan vents the radon-laden air safely outdoors[7].
Aeration removes 95–99% of radon. It is the most effective option for high levels (above 4,000 pCi/L).
Requires: Professional installation. Electrical connection. Exterior vent. Annual maintenance is minimal — check the fan and clean the tank yearly.
Granular Activated Carbon Tank ($1,000–$2,500)
A GAC tank adsorbs radon onto carbon as water flows through. It removes 90–95% of radon[7].
Important: The carbon becomes slightly radioactive over time as it collects radon. Spent carbon must be disposed of properly. Replace the media every 3–5 years ($200–$400).
Best for: Moderate radon levels (300–4,000 pCi/L). For very high radon, aeration is the better choice.
What Does NOT Remove Radon
- Water softeners do not remove radon.
- Standard sediment or iron filters do not remove radon.
- Reverse osmosis has limited radon removal and only treats one faucet.
- Boiling water releases radon into your kitchen air — making exposure worse[9].
DIY vs. Professional Installation
Both aeration and GAC systems require professional installation. These are point-of-entry systems on your main water line. They involve plumbing, electrical work, and venting.
Professional installation costs $500–$1,500 depending on complexity. Choose a contractor experienced with radon water treatment.
What to Do Next
Live in a high-radon area? Test your water and indoor air. The EPA radon zone map shows risk by county[5]. Granite states (NH, ME, VT, CT, PA) should test routinely.
Have test results? Use our Water Test Interpreter for a treatment plan.
Also have other contaminants? Read our Best Whole House Filters comparison. Radon treatment works alongside iron and manganese systems.
Frequently Asked Questions
Is radon in well water dangerous?
Yes. Radon is the #1 cause of lung cancer among non-smokers[5]. It escapes from water into indoor air during showers and other water use. The EPA estimates radon in water causes about 168 cancer deaths per year[3].
What is the EPA limit for radon in water?
The EPA proposed MCL is 300 pCi/L, but it has not been finalized[2]. An alternative MCL of 4,000 pCi/L applies in states with indoor radon programs. Most experts recommend treating above 4,000 pCi/L as a priority.
How much does radon water testing cost?
$40–$150 at a certified lab. Standard well water tests do not include radon — you must request it separately. The sample must be collected carefully to avoid releasing the gas[8].
How do you remove radon from water?
Aeration ($3,000–$5,000) removes 95–99% by venting radon gas outdoors. GAC tanks ($1,000–$2,500) adsorb radon onto carbon[7]. Both require professional installation.
Does boiling water remove radon?
Boiling releases radon from water directly into your kitchen air. This makes exposure worse, not better[9]. Never boil water as a radon treatment.
References
- U.S. EPA. "Drinking Water from Private Wells: Radon." 2024. https://www.epa.gov/radon/radon-drinking-water
- U.S. EPA. "Proposed Radon in Drinking Water Rule." 40 CFR Part 141, 2024. https://www.epa.gov/radon
- National Research Council. "Risk Assessment of Radon in Drinking Water." National Academies Press, 1999.
- U.S. Geological Survey. "Radon in Ground Water." National Water-Quality Assessment Program, 2023. https://www.usgs.gov/mission-areas/water-resources
- U.S. EPA. "A Citizen's Guide to Radon." EPA 402/K-12/002, 2024. https://www.epa.gov/radon
- CDC/ATSDR. "Radon Toxicological Profile." Agency for Toxic Substances and Disease Registry, 2023. https://www.atsdr.cdc.gov
- Water Quality Association. "Point-of-Entry Treatment for Radon in Water." Technical Brief, 2024. https://wqa.org
- University of Maine Extension. "Radon in Well Water: Testing and Treatment." Bulletin 6023, 2023.
- New Hampshire Department of Environmental Services. "Radon in Drinking Water." Fact Sheet WD-DWGB-3-12, 2023.
- American Lung Association. "Radon." 2024. https://www.lung.org/clean-air/at-home/indoor-air-pollutants/radon