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Radon in water
How radon gets into water, who it affects most, how a water test differs from an air test, and how elevated water radon is treated.
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Radon in well water: which wells, the risk, and what to do
Short answer
Radon in well water comes from uranium in the rock a well is drilled into, and wells in granite and similar rock can carry thousands of picocuries per liter, while surface water rarely does. Because radon escapes into the air whenever the water is used, well owners should test both the air and the water, and treat the water at the point of entry if it is high.
Next step: find out how well water is tested and treated. Radon in water
Key takeaways
- Wells drilled into or near uranium-bearing rock, such as granite, can pick up radon; shallow dug wells and surface water usually carry less.
- Two neighboring wells can test very differently, and one well can change through the year.
- Radon leaves the water when it is used: showers, laundry and dishwashers release it into the air you breathe.
- Test the air and the water. Vermont and Maine use 4,000 pCi/L in water as the point to act or look harder.
- The fixes are aeration or whole-house granular activated carbon, installed where the water enters the house.
Why well water carries radon
Radon in well water starts in the rock. Radon comes from the decay of uranium in the earth's crust, and can get into drinking water when a well is drilled into or near rock formations that contain uranium. Groundwater from springs, wells and boreholes normally has higher radon concentrations than surface water from reservoirs, rivers or lakes, because surface water in contact with the air lets radon escape.
Agency estimate
200 to 600 pCi/L
EPA's estimate of the average radon concentration in U.S. groundwater; granite aquifers may average more than 8,000 pCi/L
Which wells are most likely to have radon
Geology and well type decide most of it. In Georgia, for example, wells drilled into granitic crystalline rock aquifers, mostly above the Fall Line, are at risk, because that is where the uranium that decays to radon is found at higher levels, while aquifers in the south of the state are mainly limestone. Shallow dug or bored wells are often not deep enough to reach water in contact with concentrated uranium or radon.
| Well or supply | Detail |
|---|---|
| Drilled well in granite or other crystalline rock | At risk; granite aquifers may average more than 8,000 pCi/L |
| Drilled well near rock containing uranium | Radon can get into the water |
| Shallow dug or bored well | Often too shallow to reach concentrated uranium or radon sources |
| Small public groundwater system | Limited survey data suggest smaller systems have higher concentrations than larger ones |
| Private well, any area | Test it; Maine, for one, recommends it for all homes with wells |
The highest radon concentration reported from a Georgia well was 140,000 . Because two adjacent wells can differ widely, every drilled well in an at-risk area should be tested.
What radon in well water does in the house
The water carries radon in and the household lets it out. Taking showers, doing laundry and running the dishwasher all release it into the air. Radon escapes easily from water when it is agitated or aspirated, and many Maine homes have high air radon levels from the water alone.
| Radon in the well water | Added to indoor air, about |
|---|---|
| 2,000 pCi/L | 0.2 pCi/L |
| 4,000 pCi/L | 0.4 pCi/L |
| 10,000 pCi/L | 1 pCi/L |
| 20,000 pCi/L | 2 pCi/L |
| 140,000 pCi/L (the highest reported Georgia well) | 14 pCi/L |
A common estimate is that 10,000 pCi/L of radon in water adds about 1 pCi/L to a home's air. Soil gas usually adds more: radon entering through the soil is usually a much larger risk than radon entering through water, and even in Maine, where many homes get high air radon from the water alone, most of the radon in homes comes from soil gas.
Radon in well water and health
Breathing radon raises your lifetime risk of lung cancer, and the major danger from radon in water is lung cancer from the radon released into the air, though drinking it over a lifetime also poses a stomach cancer risk. Research has shown the lung cancer risk from breathing radon is much larger than the stomach cancer risk from swallowing water with radon in it.
What to do if you have a private well
Test the air
Test the air before deciding how to reduce radon; the air test comes first. See radon testing.
Test the water
With a lab kit or a certified drinking water lab; see water testing. Testing more than once at different times of year gives a better picture.
Compare the two
At about 10,000 to 1, work out how much of your air radon the water could explain.
Decide what to fix
Maine suggests looking at your risk from all radon sources and deciding which is most important to reduce.
Treat the water if needed
Aeration or whole-house granular activated carbon; see water treatment.
Retest
Retest the water after a treatment system is installed.
Typical radon reduction, EPA
Basement and slab-on-grade homes
- Subslab suction (subslab depressurization)50 to 99 percentWorks best if air can move easily in material under slab.
Radon in private well water
- Private well water: aeration95 to 99 percentGenerally more efficient than GAC; requires annual cleaning to maintain effectiveness and to prevent contamination; requires venting radon to outdoors.
- Private well water: granular activated carbon (GAC)85 to 95 percentLess efficient for higher levels than aeration; use for moderate levels, around 5,000 pCi/L or less in water.
Radon in well water levels: when to act
| Result | Vermont | Maine |
|---|---|---|
| Below 4,000 pCi/L | You do not need to treat your water; test again in five years | Below the 4,000 pCi/L Maximum Exposure Guideline |
| At or above 4,000 pCi/L | Take action to reduce radon in your home | Look at the risk from all radon sources and decide which to reduce |
| Around 10,000 pCi/L and up | Take action | Strongly consider fixing the water, as well as any radon in air from soil gas |
Maine is explicit that its guideline is not a line to fix at: the MEG does not mean you should fix the water at 4,000 pCi/L, but the higher the result rises above it, the more important treatment becomes. UGA Extension's lab bands are on water testing.
Radon in well water mitigation
A radon in water problem in a private well can be easily fixed. Whole-house, point-of-entry treatment removes radon before the water enters the home's pipes, usually with aeration or granular activated carbon. The point of entry matters because radon can be released anywhere water is used in the home, so it should be removed at or before the point the water enters.
| Feature | Aeration | Granular activated carbon |
|---|---|---|
| How it works | Mixes water with air in a tank and vents the air and radon outdoors | Traps radon on activated carbon until it decays |
| Typical reduction | 95 to 99 percent | 85 to 95 percent |
| When it fits | Above 10,000 pCi/L | Around 5,000 pCi/L or less; Vermont discourages it for radon |
| Installed cost, Georgia extension estimate | ~$4,000 installed | ~$1,000 installed |
A soil-gas system does not touch the water, and a water system does not touch soil gas. If your air is high from the soil, see radon mitigation.
Help paying for well water treatment
Some states help. Vermont, for example, offers funding to help pay for water treatment or to fix a water system, depending on eligibility, and its health department laboratory runs a study that gives some well owners free test kits while they last. Ask your state's drinking water or radon program what it offers.
Buying or selling a home with a well
If the air has been tested and is high and the home has a private well, have the water tested. States may set rules for who tests: in Maine, it is illegal for a realtor or home buyer to do a radon in air or radon in water test, and a home for sale needs an independent registered radon tester.
Radon in well water questions
Can radon get into a house through well water?
Yes. Radon dissolved in well water is released into the air when water is used for showers, laundry and dishes; see also does radon come from well water.
How do I know if my well has radon?
Test it. You cannot see, smell or taste radon. See how to test for radon in well water.
What is a high radon level in well water?
Vermont's advisory level is 4,000 pCi/L, and Maine's guideline is the same figure, with treatment strongly considered around 10,000 pCi/L.
Does a deeper well have more radon?
Shallow dug or bored wells are often not deep enough to reach water in contact with concentrated uranium or radon, while drilled wells in granite are at risk.
If my air radon is high, is my well the cause?
Not necessarily. Soil gas radon does not predict well water radon, and soil gas is usually the larger source. Test both.
Can radon in well water change?
Yes. Levels can vary through the year, so test more than once at different times.
How is radon removed from well water?
With aeration or whole-house granular activated carbon at the point of entry; see how to get radon out of water.
How often should I retest my well?
Vermont's advice is to test again in five years if the result is under 4,000 pCi/L, and to retest after installing a treatment system.
Questions people ask
Can radon get into a house through well water?
It can: groundwater from wells normally carries more radon than surface water, and some of that radon escapes into the indoor air when the water is used for showers and other household purposes. Radon from the soil is usually a much larger risk than radon from water, though, so the first test is of the air.
How do you test well water for radon?
Test the air first, then, if you have a private well, have the water tested: a sample is collected and sent to a lab that measures its radon, using different devices and procedures from an air test. Your state radon office or the Safe Drinking Water Hotline can point you to a lab.
How is radon removed from well water?
Radon is removed from water with point-of-entry treatment, which treats all the water before it reaches the taps, usually by aeration, which typically removes 95 to 99 percent, or a granular activated carbon filter, which typically removes 85 to 95 percent. A filter at a single tap does not address radon released into the air.
Water
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Radon in well and household water: when it matters, how a water test works, and treatment.
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How aeration and granular activated carbon systems reduce radon in water, and how they differ from soil-gas mitigation.
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