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How do you test for radon in well water?

By Radon411 Editorial TeamUpdated How we research

Short answer

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.

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

Radon in a home's air comes from two main sources, the soil and the water supply, and the soil is usually the much larger risk. That is why the air test comes first; if it finds a radon problem and your water comes from a well, test the water next.

Groundwater from wells normally carries more radon than surface water, and radon dissolved in water is released into indoor air when the water is used. Most of the risk from radon in water comes from that release during showering and other household use.

Water sampling follows its own protocol, MW-RN-2020, which covers collecting and transporting water samples and transferring them to a measurement device. Follow the lab's collection instructions exactly.

What to do next: test the air in the lowest lived-in level if you have not. If you have a private well, ask your state radon office which labs measure radon in water, and if the result is high, look into point-of-entry treatment.

Test the air first, then the well

A home's indoor radon has two main sources, the soil and the water supply, and radon from the soil is usually a much larger risk. So the order matters: test the air first. If you have tested the air and found a radon problem, and your water comes from a well, have your water tested.

Which homes should test their water for radon
Water sourceRadon in water likely?What to do
Private wellMore likely: the water is groundwaterTest the air, then test the water, especially if the air is high
Public supply that uses groundwaterMore likelyContact your water supplier
Public supply from surface waterNot usually a problemTest the air

Well owners can also test both at once. Testing air and water together gives a fuller picture of which radon options suit the home.

Why well water can carry radon

Groundwater from springs, wells and boreholes normally has higher radon concentrations than surface water from reservoirs, rivers or lakes. Radon dissolved in water is released into indoor air when the water is used, so most of the risk from radon in water comes from breathing it after showering and other household use, not from drinking it.

How a well water test works

A water test is not an air test with a different label. The devices and procedures for testing water are different from those for measuring radon in air. A sample of water is collected and carried to a device that measures how much radon it holds.

  1. Get a water test kit or lab

    Ask your state radon office which laboratories measure radon in water, or call the Safe Drinking Water Hotline at (800) 426-4791.

  2. Collect the sample as instructed

    Follow the lab's collection steps exactly; the result is only as good as the sample.

  3. Send it promptly

    Return the sample as the lab directs, so it reaches the measurement device as the protocol expects.

  4. Compare with your air result

    Read the water result next to your air test to decide what, if anything, to fix.

The standard for water sampling
StandardWhat it covers
MW-RN-2020Protocols for the collection, transfer and measurement of radon in water: collecting and transporting water samples, and transferring the sample to a measurement device

If the water result is high

A radon in water problem in a private well can be fixed. Treatment at the point of entry removes radon before the water reaches the home's taps, usually with aeration or a granular activated carbon filter.

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 reduction for the two point-of-entry water treatments.

Aeration typically removes 95 to 99 percent and granular activated carbon 85 to 95 percent. See how to get radon out of water for how the two compare.

Wells, public water and the air test

Some public water systems treat their water to reduce radon before it is delivered, so a home on a public supply that worries about radon in its water should start with the supplier. For any home, the air test in the lowest lived-in level comes first, because that is where most of the radon risk is.

Questions about testing well water for radon

Should I test my well water for radon?

Yes, if you are on a private well, especially after an air test shows a radon problem. Test the air first.

Can I use an air test kit for water?

No. The devices and procedures for testing water are different from those used for air.

Where do I get my well water tested for radon?

Ask your state radon office which labs measure radon in water, or call the Safe Drinking Water Hotline at (800) 426-4791.

Is radon in well water dangerous to drink?

The main risk is breathing radon released from the water into the air. The stomach cancer risk from swallowing it is much smaller than the lung cancer risk from breathing radon in air.

Does city water have radon?

Water from surface sources is not usually a problem. Public systems that use groundwater are more likely to carry radon, and some treat it; contact your supplier.

What if my well water has high radon?

It can be fixed with point-of-entry treatment, usually aeration or a granular activated carbon filter.

Water

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