Overview page
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.
At a glance · 1 min read
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 |
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- Cracks in solid floors
- Construction joints
- Cracks in walls
- Gaps in suspended floors
- Gaps around service pipes
- Cavities inside walls
- The water supply
Step by step · 1 min read
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.
Step 1 of 5:
Test the air
With a short-term or long-term air test; see radon testing.
Step 2 of 5:
Check your water source
Private well, public groundwater supply, or surface water. Radon in water is not usually a problem from surface water.
Step 3 of 5:
Public supply?
If you are concerned, contact your water supplier; some public systems treat their water for radon.
Step 4 of 5:
Private well?
Order a water test from your state lab, a certified drinking water lab or your extension service.
Step 5 of 5:
Compare the results
Use both numbers to decide what, if anything, to fix.
Read moreA note, 1 min
At a glance · 1 min read
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 |
Read moreA paragraph, 1 min
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.
In a picture · 1 min read
How a water sample is taken: the steps and the standard
A water sample is taken so that the radon stays in it. The Vermont Health Department Laboratory's instructions for its radon in water kit, which comes with two 40 mL glass vials, are a clear example of the steps: the vials are filled from one cold-water tap, to overflowing, with no air bubble of any size, and returned to the laboratory within 48 hours of collection.
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- Take off the aerator. Remove the aerator or strainer from the faucet, if possible. Do not touch the inside of the cap or the mouth of a vial.
- Run the cold water. Let the cold water run at full flow for 3 to 5 minutes, then turn it down to low flow.
- Fill both vials to overflowing. Fill both 40 mL vials from the same tap until they overflow, and tighten each cap firmly.
- Check for bubbles. Turn each vial over and tap it gently. If there are air bubbles of any size, empty the vials and collect again.
- Record the time, return in 48 hours. Write down the date and time you collected the sample, and get it back to the laboratory within 48 hours.
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Read moreTwo paragraphs, 1 min
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
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.
At a glance · 1 min read
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 |
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Read moreA paragraph, 1 min
For the step-by-step question, see how to test for radon in well water.
At a glance · 1 min read
Reading a radon water test result
Results come in
| 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 |
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Read moreA paragraph, 1 min
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.
At a glance · 1 min read
State guidance for radon in well water
There is no federal limit for private wells, so the numbers a well owner reads a result against come from states. These are the levels four state and university programs publish, beside the 1999 EPA proposal that the 300 and 4,000 pCi/L figures come from. A level here is a point to act or look harder, not a line between safe and unsafe.
| Program | Level | What it says to do |
|---|---|---|
| Connecticut Department of Public Health | 5,000 pCi/L, its recommended action level | Take action if the average of two water samples, drawn at the same time from the same place, is at or above 5,000 pCi/L |
| Maine CDC | 4,000 pCi/L, its Maximum Exposure Guideline | Weigh all your radon sources, soil gas and water, and decide which is most important to reduce; around 10,000 pCi/L, strongly consider fixing the water |
| Vermont Department of Health | 4,000 pCi/L, its advisory level | Below it, no need to treat; test again in five years. At or above it, take action to reduce radon |
| University of Georgia Extension | 300, 4,000 and 10,000 pCi/L bands | Below 300 low; 301 to 4,000 treatment may be considered; above 4,000 a whole-house system is recommended, aeration above 10,000 |
| EPA, 1999 proposed rule (not for private wells) | 300 pCi/L, or 4,000 pCi/L with an indoor air program | Proposed for community water systems that use groundwater; EPA does not regulate private wells |
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Read moreA paragraph, 1 min
Because the levels differ, read your result against your own state's guidance where it publishes one, and ask your state radon or drinking water program where it does not. The radon in water overview explains where the 300 and 4,000 pCi/L figures come from.
At a glance · 1 min read
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 |
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Read moreA paragraph, 1 min
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.
Questions · 1 min read
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.
How do you collect a radon water sample?
Follow your lab's own kit instructions. Vermont's lab, for example, says to remove the aerator if possible, run the cold water at full flow for 3 to 5 minutes, fill both vials at low flow until they overflow, cap them, and check for bubbles: if there are air bubbles of any size, empty the vials and collect again. Samples go back to the lab within 48 hours.
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
Questions people ask
Short answers. Each one links to the page with the full answer.
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.
Open the page