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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 water test: how to test water for radon and read the result
Short answer
A radon water test is a sample of your water analyzed by a laboratory, collected and handled by procedures that differ from those for an air test. Test the air first and, if it is high and you have a private well, have the water tested; some states recommend testing every well, and testing more than once at different times of year gives a better picture.
Next step: find out how well water is tested and treated. Radon in water
Key takeaways
- A water test measures radon dissolved in your water, in pCi/L, from a sample analyzed by a lab.
- It uses different devices and procedures from an air test. An air test kit does not measure water.
- Test the air first; then test the water if the air is high and you are on a private well. Some states recommend testing every well.
- Radon in well water varies through the year, so more than one test, at different times, gives a better picture.
- Read the result against your air result: about 10,000 pCi/L in water adds about 1 pCi/L to the air.
What a radon water test is
A radon water test measures how much radon is dissolved in a home's water. You cannot see, smell or taste radon, and testing is the only way to know if it is in your drinking water. The devices and procedures for testing a water supply are also different from those used for measuring radon in air.
| Feature | Air test | Water test |
|---|---|---|
| What it measures | Radon in the air, in pCi/L | Radon dissolved in water, in pCi/L |
| Typical result scale | The action level is 4 pCi/L | Vermont's advisory level is 4,000 pCi/L |
| How it is done | A device left in the lowest lived-in level for at least 48 hours | A water sample collected and sent to a lab |
| Who needs it | Every home below the third floor | Homes on private wells, especially if the air is high |
- Cracks in solid floors
- Construction joints
- Cracks in walls
- Gaps in suspended floors
- Gaps around service pipes
- Cavities inside walls
- The water supply
Who should test water for radon, and in what order
EPA's Citizen's Guide says that although radon gets into some homes through water, it is important to test the air first, and that if you find a radon problem in the air and your water comes from a well, you should have the water tested. Vermont gives the same order: if the air has not been tested, test it before considering how to reduce radon. Maine goes further and recommends that all homes with wells test for water radon.
Test the air
With a short-term or long-term air test; see radon testing.
Check your water source
Private well, public groundwater supply, or surface water. Radon in water is not usually a problem from surface water.
Public supply?
If you are concerned, contact your water supplier; some public systems treat their water for radon.
Private well?
Order a water test from your state lab, a certified drinking water lab or your extension service.
Compare the results
Use both numbers to decide what, if anything, to fix.
Where to get a radon water test
| Program | What it offers |
|---|---|
| Vermont Department of Health Laboratory | A radon in water test kit for $25; a lab study that gives free test kits for wells or springs while a limited number last; or use another certified drinking water lab |
| University of Georgia Extension | Tests for uranium and radon in drinking water; contact your county Extension office for sampling and submission details |
| Your state radon or drinking water program | Your state radon office can help with radon in water testing and treatment |
Air test kits sold in stores measure air, not water. For a list of air kits and free state kit programs, see radon test kits and free radon test kits.
How a water sample is taken: the standard
Professionals follow a written protocol: ANSI/AARST MW-RN-2020, Protocol for the Collection, Transfer and Measurement of Radon in Water, which sets minimum requirements for measuring radon in water that enters a building through groundwater, to decide whether is needed. It covers how samples are collected and transported and how the sample is transferred to a measuring device.
It can also be worth testing the water for uranium and radium, using a gross-alpha measurement, because they may be present and may be more hazardous to health.
When and how often to test water for radon
| When | Why |
|---|---|
| After an air test shows high radon, if you have a private well | The water may be one of the sources |
| Any home with a well | Soil gas radon does not predict well water radon |
| More than once, at different times of year | Levels in well water vary through the year |
| Every five years if the result is under 4,000 pCi/L | The interval Vermont advises |
| After a treatment system is installed | To confirm the system works |
| Every drilled well in an at-risk area | Adjacent wells can differ widely |
For the step-by-step question, see how to test for radon in well water.
Reading a radon water test result
Results come in of water, and the numbers are much larger than air results. One state extension lab reads them in four bands, and Vermont and Maine use 4,000 pCi/L as their reference point.
| Result | Reading | Suggested treatment |
|---|---|---|
| Below 300 pCi/L | Low; no considerable health risk from ingestion | No treatment |
| 301 to 4,000 pCi/L | Slightly elevated; may not pose a significant health risk | Treatment may be considered; a whole-house carbon system |
| 4,000 to 10,000 pCi/L | Significant risk from ingestion; may significantly raise indoor air radon | Whole-house carbon or aeration recommended |
| Above 10,000 pCi/L | Significant risk from ingestion; may significantly raise indoor air radon | Whole-house aeration recommended |
Vermont treats a result under 4,000 pCi/L as not needing treatment, with a retest in five years, and calls for action at or above 4,000 pCi/L. Maine's 4,000 pCi/L guideline is a point to weigh all your radon sources rather than a line to fix at, with treatment strongly considered around 10,000 pCi/L. To see what your number adds to the air, use about 10,000 pCi/L in water to 1 pCi/L in air.
Water and air results together
| Air result | Water result | What to do |
|---|---|---|
| 4 pCi/L or more | Low | The soil is the likely source; fix the air with a soil-gas system |
| 4 pCi/L or more | 10,000 pCi/L or more | Both may matter; weigh each source |
| Under 4 pCi/L | 4,000 pCi/L or more | Act on the water; 4,000 pCi/L is Vermont's advisory level |
| Under 4 pCi/L | Low | Retest the air in the future and the water in five years |
Soil gas radon does not predict well water radon, nor the reverse, so one result never stands in for the other. Treatment options are on water treatment, and air fixes on radon mitigation.
Radon water testing questions
How do you test water for radon?
Order a water test from a state laboratory, a certified drinking water lab or an extension service, and collect the sample exactly as its instructions say.
Can I use an air radon test kit to test water?
No. The devices and procedures for testing water are different from those for air.
How much does a radon water test cost?
Prices vary by lab. Vermont's Health Department Laboratory, for example, sells a radon in water test kit for $25. See also radon testing cost.
Should I test my water if my air radon is low?
Yes, if you are on a well. Air and water radon are separate, and some states, Maine among them, recommend that every home with a well test its water.
What is a normal radon level in well water?
EPA estimates that average radon in U.S. groundwater is 200 to 600 pCi/L; granite aquifers can average more than 8,000 pCi/L.
How often should well water be tested for radon?
Every five years if the result is under 4,000 pCi/L, which is Vermont's advice; after any treatment system is installed; and more than once, at different times of year, at the start.
Who tests water for radon?
State health laboratories, certified drinking water labs and some university extension services. Some states also license radon testers.
Do I need to test public water for radon?
Ask your supplier. Some public systems that use groundwater treat for radon, and surface water is not usually a problem.
Questions people ask
How is drinking water tested 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.
Should drinking water be tested for radon?
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.
Water
Related guides
Radon in well and household water: when it matters, how a water test works, and treatment.
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Well water and radon
Why private wells are the main concern for waterborne radon, and what public water treatment changes about that risk.
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Water treatment for radon
How aeration and granular activated carbon systems reduce radon in water, and how they differ from soil-gas mitigation.
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