Radon in Well Water: What Your Test Result Means and When to Treat It
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- Radon is a radioactive gas from uranium in rock. Wells drilled into granite and other bedrock are the most likely to have it.
- There is no federal limit for private wells. Many states act at 4,000 pCi/L in water.
- Most of the risk comes from radon released into indoor air, so test the air as well as the water.
- Aeration is the standard fix for high levels. A typical system costs about $3,500.
Radon in well water sounds scary, and the numbers on a lab report do not help. A result of 2,000 pCi/L looks huge until you know how the scale works.
In this guide I explain what your number means, when to treat the water, and when the air in your house is the bigger problem. Use the checker below with the result from your lab report.
Radon in water result checker
Type the number from your lab report. Add your air test if you have one.
Your result will show here.
What radon in well water is
Radon forms when uranium in rock and soil breaks down. Groundwater that sits in that rock picks up the gas, and your pump brings it into the house.
When the water hits the air at a shower head, washing machine or dishwasher, the radon escapes. That is why EPA’s own analysis found that breathing radon from water causes far more of the risk than drinking it.
Wells in bedrock, especially granite, tend to have higher levels than shallow wells in sand and gravel. The only way to know your number is to test.
Radon levels explained
| Radon in water | What it means | Adds to indoor air |
|---|---|---|
| Below 300 pCi/L | Low. Below the 1999 EPA proposal for public systems. | Under 0.03 pCi/L |
| 300 to 3,999 pCi/L | Moderate. Test the air and fix that first if it is high. | 0.03 to 0.4 pCi/L |
| 4,000 to 9,999 pCi/L | High. Many states advise treating the water. | 0.4 to 1 pCi/L |
| 10,000 pCi/L and up | Very high. Aeration is the standard fix. | 1 pCi/L or more |
Air figures use the 10,000 to 1 rule of thumb implied by EPA’s figures (4,000 pCi/L in water adds about 0.4 pCi/L to air). EPA’s action level for radon in air is 4 pCi/L.
How to test your well for radon
- Test the air first. Wisconsin DNR advises an air test first, since air carries most of the risk. A short term kit that says it meets EPA requirements costs little at most hardware stores.
- Order a radon in water kit. Get one from your state lab or a certified drinking water lab. Vermont’s state lab charges $25.
- Take the sample right. Run a cold tap that has not been through a filter, then fill the vial with no air bubbles, as the kit says.
- Ship it fast. Radon has a half life of about 3.8 days, so a slow sample reads low.
- Test again. Levels change through the year, so Vermont suggests more than one test at different times.
See radon in water test kits on Amazon See home radon air detectors
Testing for other things at the same time makes sense. My well water testing schedule shows what to test and when, and the best well water test kits guide covers the general kits.
Treatment options compared
| Option | How it works | Best for | Watch out for |
|---|---|---|---|
| Aeration system | Mixes water with air in a tank, a fan vents radon outside | High and very high levels | Cost about $3,500 (Wisconsin DNR); iron and hardness can foul it |
| Granular activated carbon tank | Carbon holds the radon as water passes through | Lower levels, often with pretreatment | Used carbon can become a radiation hazard; Vermont discourages it |
| Air mitigation | Sub slab fan pulls soil gas out from under the house | High air radon from soil | Does not lower radon in the water itself |
| Bottled water | Cuts what you drink | Short term only | Radon still escapes in showers and laundry |
What to do, step by step
- Test the air in your home.
- Test the water at a certified lab and put the result in the checker above.
- If air is above 4 pCi/L, fix the air first. It is usually the bigger risk.
- If water is at or above 4,000 pCi/L, get quotes for an aeration system from a certified installer.
- Retest the water after the system is installed to confirm it works.
Radon is one of several things a private well can carry. Read about arsenic, lead and PFAS in well water too.
Frequently asked questions
What is a safe level of radon in well water?
There is no federal limit for private wells. EPA proposed 300 pCi/L for public systems in 1999, with a 4,000 pCi/L alternative for states with indoor air programs, and the rule was never finalized. Many states, including Vermont and Wisconsin, use 4,000 pCi/L as the point to act.
Is radon in well water dangerous to drink?
Most of the risk comes from breathing it, not drinking it. EPA estimated that about 89% of the cancer deaths linked to radon in water come from lung cancer after radon escapes into indoor air, and about 11% from stomach cancer from drinking it.
How much does radon in water add to indoor air?
A common rule of thumb is 10,000 to 1. Water at 10,000 pCi/L adds about 1 pCi/L to the air in your home, mostly from showers, laundry and dishwashers.
How do you remove radon from well water?
An aeration system is the usual fix. It mixes water with air in a tank and vents the radon outside. Wisconsin DNR puts a typical system at about $3,500. Granular activated carbon can work at lower levels, but the used carbon can become radioactive.
How do I test my well for radon?
Use a radon in water kit from your state lab or a certified drinking water lab. The sample must be taken with no air bubbles and shipped quickly, because radon decays with a half life of about 3.8 days.
Does a water softener or filter pitcher remove radon?
No. Softeners and small faucet or pitcher filters are not designed for radon. Wisconsin DNR notes that small faucet or under sink filters are not adequate.
Sources: EPA, proposed radon in drinking water rule Q and A; Wisconsin DNR, radon in private well water; Vermont Department of Health, radon in drinking water. All checked 12 November 2026.
