How to Test for Radon in Well Water (And What Your Results Mean)

Radon in well water is tested by a certified lab. You get a small sample vial from the lab, fill it at a cold tap with no air bubble in it, and mail it back right away, because radon is a gas and it leaves the water if the sample splashes or sits. Before you do that, test the air in your house. Radon you breathe is the bigger risk, and the air number tells you whether the water number matters. A short-term air kit sits out 2 to 4 days and costs about $20; a radon water test runs $25 to $129 depending on who sells it, and our lab reports in about 8 business days.

Why test the air before the water?

Test the air first, because every 10,000 pCi/L of radon in your well water adds only about 1 pCi/L to the air in your house. That is the rule of thumb the EPA, the National Radon Program Services and the Connecticut and North Carolina radon programs use. Radon from the soil under the house is the main source; the National Radon Program Services puts the share of indoor radon that comes from water at only about 1 to 2 percent.

The water still matters on a well. When you shower, run the dishwasher or do laundry, the radon in the water comes out into the air you breathe. The EPA estimates radon in drinking water causes about 168 cancer deaths a year, 89 percent of them lung cancer from breathing the radon that came out of the water and 11 percent stomach cancer from drinking it. The EPA recommends that every home on a private well test the water for radon, and its own guidance says to test the air first.

The two numbers only mean something together. Say your water tests at 30,000 pCi/L. By the rule of thumb, about 3 pCi/L of your indoor reading may be coming from the water. If your air reads 12, the foundation is the main problem and the house gets fixed first. If your air reads 4.5, the water could be what puts you over the 4 pCi/L line.

Radon can differ from one well to the next, even between neighbors, so a ZIP code map cannot give you your well's number. The rock your well is drilled into matters: the EPA's average for groundwater is 200 to 600 pCi/L, and wells in granite can run over 8,000. People call me from Maine, New Hampshire and North Dakota with radon on their minds ("we got radon in certain areas out here too," one caller told me), but the only way to know your own well's number is to test it.

Short-term vs long-term air kits

A short-term kit tells you in a few days whether you have a radon problem; a long-term kit tells you your year-round average. Radon in a house changes from day to day and season to season, and it is usually highest in the heating season, so one short test is a snapshot.

The EPA's advice is to start with a short-term test. A result of 4 pCi/L or higher gets a second test, with another short-term kit or a long-term kit, before you hire anyone. A short-term kit only reads right if you set it up the way the lab says:

• Close the windows and outside doors at least 12 hours before you start, and keep them closed except for coming and going.
• Put it in the lowest room you use every day, 2 to 6 feet off the floor, not in the kitchen, a bathroom or the garage.
• Do not start a 2 or 3 day test during a bad storm or very high winds.
• Write down the start and end date and time, seal it, and mail it right away. Most labs have to receive it within 10 days of the end of the test.

Plug-in digital radon monitors are handy for watching the trend, but the Wisconsin health department notes most consumer models are not approved by the national radon proficiency programs because they cannot be calibrated. For a number you act on, use a lab kit.

Where to get a radon air kit

You can get a radon air kit from your state, from the National Radon Program Services, from a home improvement store or online, and some states give them away. The EPA lists these sources:

1. Your state or county health department. Some state radon programs and local health departments hand out free or discounted kits. Start here, because free is free.
2. The National Radon Program Services at Kansas State University. Their kit order page sells a short-term kit (2 to 4 days) for $20 and a long-term kit (3 to 12 months) for $30, lab analysis and return included. Their kits take 1 to 2 weeks to arrive.
3. A home improvement store or online. North Carolina's radon program says radon kits online or at home improvement stores run $20 or less. Check whether the lab fee is in the price before you buy.
4. A radon lab. Labs sell their own kits directly, for example a charcoal canister for $35 or a long-term electret for $50 from RTCA.

We do not sell radon air kits. We sell the water test.

How to take a radon water sample

A radon water sample has to be filled under water or with no splash, capped with no air bubble, and shipped the same day. Follow the instructions in your kit first. These are the steps the radon lab AccuStar gives, condensed from the EPA's radon testing protocols.

1. Pick a cold tap

   Take the aerator or any faucet filter off the tap. If you have a carbon filter, sample from a tap ahead of it, because carbon traps radon and you would be testing the filter, not the well.

2. Run the cold water first

   Let the cold water run until fresh water from the well is coming through. Water that sat in the pipes or a holding tank has already lost some of its radon.

3. Fill the vial under water

   Slowly fill a bowl or a deep pan with the spout under the water so it does not splash. Put the open vial and its cap under the water until they fill, then screw the cap on tight while both are still under water.

4. Check the vial for bubbles

   Lift it out and turn it upside down. If you see any bubble or air space, dump it and fill it again. AccuStar says a vial missing about a dime's worth of water is thrown out as invalid.

5. Ship the vial the same day

   Write the date and time you filled it on the form; the lab needs it to figure your result. Ship it the same day. AccuStar has to receive the vial within 7 days of sampling (4 days for Connecticut and New York). Our radon test comes with the prepaid return label.

Radon in a well changes through the year, so Vermont and Connecticut both suggest testing more than once, at different times, before you decide anything.

What your radon number means

There is no federal limit for radon in a private well, so the levels you will see come from your state. Radon in water is reported in picocuries per liter (pCi/L), the same unit as air, which confuses people: 4 is the line for air, and water numbers run in the thousands. The EPA once proposed a limit for public water systems of 4,000 pCi/L in states with an indoor air radon program, or 300 pCi/L without one. It was never made final, and the EPA does not regulate private wells.

Check with your own state's radon program, since the levels differ. A caller in New Hampshire read me the radon line off a lab report: "the radon was 1,170. Uh, so I don't know." That is below every state level in the table, and by the 10,000-to-1 rule it adds about 0.1 pCi/L to the air in the house.

Got a radon number for air or water?

Text Aidan your radon result

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Text Aidan443-277-2204 Call800-460-5810Aidan

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Why radon is not on a well test

Radon is not on our $199 well test. It needs its own sealed vial, mailed to the lab fast. Radon is a gas, and it escapes from an ordinary sample bottle, so it needs its own vial filled and capped with no air in it. If your report has no radon line, your well was not tested for radon, even if the test was called complete.

I still tell people to test before they buy anything, and the $199 well test covers the rest: 53 contaminants, including uranium and arsenic. In this video I walk through how that mail-in test works and what I look at first when the results come back.

If you only need the one number, our uranium test is $89 and the radon test is $129. For the full baseline, see how to test well water, and once you have a report, how to read well water test results.

What removes radon from well water?

Radon comes out of well water with a whole-house carbon tank at lower levels or an aeration system at high levels, and either one has to treat all the water coming into the house, not just the kitchen tap, because the risk is the radon you breathe. When a customer's test shows radon, "we use carbon tanks," and the one I recommend is a 2.5 cubic foot non-backwashing carbon tank, like the Clack 2.5 cubic foot carbon filter ($1,695).

The University of Georgia's extension service puts carbon at better than 95 percent removal when radon is under 30,000 pCi/L, and Connecticut says carbon works well below 10,000. Carbon has one catch: radon's decay products build up in the carbon, so the carbon gets replaced on a schedule and the tank is best kept away from living space. Aeration bubbles air through the water and vents the radon outside, up to 99 percent removal. We do not sell a radon aeration system. More on carbon tanks in carbon filters for well water.

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