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Does radon come from well water?

By Radon411 Editorial TeamUpdated How we research

Short answer

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.

Next step: find out how well water is tested and treated. Radon in water

Most of the risk from radon in water comes from breathing the radon it releases, not from drinking it: the lung cancer risk from breathing radon is much larger than the stomach cancer risk from swallowing it. Studies have not confirmed a link between drinking radon in water and stomach cancer.

The source of the water matters. Radon in water is more likely in private wells and in public supplies that use groundwater, and is not usually a problem when the source is surface water, which is where most public supplies come from. Some public systems treat their water for radon before it is delivered.

If the air level is high and your home is on a private well, test the water as well; water tests use different devices and procedures from air tests. Point-of-entry treatment, by aeration or granular activated carbon filters, removes radon before the water reaches your taps, while a device at a single tap treats only a small share of the water.

What to do next: test the air in the lowest lived-in level, and if you are on a private well and the result is high, ask your state radon office about testing the water.

How radon ends up in a well

Radon forms in rock and soil, and it is found in groundwater too. That is why the source of your water matters. Springs, wells and boreholes draw groundwater, which normally carries more radon than surface water from reservoirs, rivers and lakes. Radon in water is not usually a problem when the source is surface water.

Water sources and how likely radon is
Water sourceRadon in the water
Private wellMore likely: it draws groundwater
Public supply that uses groundwaterMore likely; some systems treat the water to reduce radon before delivery
Public supply from surface waterNot usually a problem; most public supplies come from lakes, rivers and reservoirs

Well water is one of the routes into a home, but not the main one: soil gas is the main cause of radon problems, and well water is a sometimes-source alongside it.

From the tap into the air

Radon dissolved in water does not stay there. When the water is used for showers and other household purposes, some of the radon escapes into the indoor air. That is where most of the risk from radon in water comes from: breathing it in, rather than drinking it.

House in cross-section showing where soil gas entersGround levelSoil and rockBasementSolid floorCrawl spaceSuspended floor1234567
  1. Cracks in solid floors
  2. Construction joints
  3. Cracks in walls
  4. Gaps in suspended floors
  5. Gaps around service pipes
  6. Cavities inside walls
  7. The water supply
Radon's routes into a home, with the water supply highlighted; the soil routes usually carry far more.
Two ways radon in water reaches you
RouteWhat is known
Breathing radon released from waterThe main risk from radon in water; the lung cancer risk from breathing radon is much larger than the stomach cancer risk from swallowing it
Drinking water with radonA small ingestion risk; studies so far have not confirmed a link between drinking radon in water and stomach cancer

How big a share comes from the water

In most homes, the water is the smaller part of the problem. Radon entering through the soil is usually a much larger risk than radon entering through the water, and a higher dose normally comes from breathing radon than from swallowing it.

If you have a private well and are concerned about radon, testing both air and water gives a fuller picture of the options for fixing it. Water tests use different devices and procedures from air tests. See how to test for radon in well water.

Treating well water for radon

A radon problem in well water can be fixed. Point-of-entry treatment removes radon before the water reaches the home's pipes, usually with aeration or granular activated carbon (GAC) filters. Point-of-use devices at a single tap treat only a small share of the water, such as what you drink, so they do not cut the risk from radon released into the air by all the water used in the home.

Typical radon reduction, EPA

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.
Typical radon removal from well water: aeration and granular activated carbon.
Aeration and carbon filters compared
AspectAerationGranular activated carbon
Typical reduction95 to 99 percent85 to 95 percent
Best forGenerally more efficient, including at higher levelsModerate levels, around 5,000 pCi/L or less in water
UpkeepAnnual cleaning; radon vented outdoorsRadioactive by-products can build up on the carbon; may need shielding and care in disposal
CostUsually costs moreUsually costs less

Both have trade-offs worth talking through with your state radon office or a water treatment professional. More is in how to get radon out of water.

If your water is from a public supply

Most public water comes from surface sources, where radon is rarely an issue. If your supply uses groundwater and you are concerned, contact your water supplier, since some systems treat their water for radon before it is delivered. For a private well, your state radon office is the place to ask.

Who to ask about radon in your water
Your waterWho to contact
Public supplyYour water supplier
Private wellYour state radon office

Questions about radon in well water

Is radon in well water dangerous?

Mostly through the air: radon released from water during showering and other uses is the main risk. Swallowing it is a small risk by comparison.

Does city water have radon?

Usually little, since most public supplies come from surface water. Supplies that use groundwater can carry radon, and some treat it; ask your water supplier.

Can you drink well water with radon?

The ingestion risk is small, and studies have not confirmed a link with stomach cancer. The larger concern is radon released into the air, which a point-of-entry system addresses.

Should I test my well water for radon?

Test the air first. If the air level is high and you have a private well, test the water as well; testing both helps you choose a fix.

Does a water filter remove radon?

Granular activated carbon filters at the point of entry typically remove 85 to 95 percent. A filter at one tap treats only a small part of the water.

Is radon from water worse than radon from soil?

No. Radon entering through the soil is usually a much larger risk than radon entering through the water.

Water

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