Radon in Well Water 2026: Causes, Testing and Removal

Radon in well water is the contaminant you cannot see, smell, or taste, which is exactly what makes it dangerous. It is a radioactive noble gas that dissolves into groundwater from uranium-bearing bedrock, and once it is in your taps it is invisible in the glass and silent in the lines. The good news: radon is measurable, it is treatable, and the EPA has published a simple decision framework that tells you exactly when treatment is justified. After testing and treating well-water systems across the western and mountain states, I can tell you that radon is the one parameter most well owners never test for until an indoor air canister forces the question. In this 2026 guide you will learn what radon in well water actually is, how to test for it (air first, water second, and why), what the EPA action and reference levels mean in plain English, and which removal methods are worth the money for a private well.

Published: September 5, 2026

What Is Radon in Well Water, and Why Should You Care?

Radon is a noble gas with the chemical symbol Rn. It forms deep underground as uranium in soil, shale, and bedrock decays, and it works its way up through fractures and porous rock into the groundwater that feeds your well. The isotope that matters to you is radon-222, with a half-life of about 3.8 days. That half-life is the reason radon is a local problem: it decays too fast to travel far, so your well only sees the radon generated in the rock immediately around the aquifer it draws from. Shallow, older wells and wells drilled in uranium-bearing geology pick up more of it. Deep, new wells in clean gravel typically pick up very little.

Most homeowners know radon as an indoor air problem, and that is fair. The EPA and the Surgeon General have identified indoor radon as the leading cause of lung cancer among non-smokers, estimated at roughly 21,000 deaths per year in the United States. But the water pathway is real and under-tested: radon that sits dissolved in your well water comes back out of solution every time you run a tap, shower, or flush a toilet, and that is where the gas re-enters your home air. In a well where water radon is elevated, a meaningful share of your indoor radon budget can be coming straight out of your own plumbing. That is why the EPA guidance for well owners is two-part: test the air, and if it is elevated, test the water to find out where the gas is coming from. You can review the full testing protocol in our well water testing guide, which covers sample handling for radon and every other parameter.

Radon Levels in Well Water: EPA Action Level, Reference Level and Risk Bands

Radon in water is measured in picoCuries per liter (pCi/L), the same unit used for indoor air. The numbers you will see on a lab report fall into a small set of bands, and the EPA assigns a specific meaning to two of them. Here is what those numbers mean in practice, and what action each one calls for.

Why the gap between 4 and 10? The 4 pCi/L line matches the indoor air action level, so if your water sits right at 4 and your home air is already elevated, the water is almost certainly a contributing source worth addressing. The 10 pCi/L line is where EPA says the water source alone is large enough that you should treat regardless of the air reading. In between, the decision hinges on your total exposure: a house that already tests 8 pCi/L in air with 3 pCi/L in the well is a more serious situation than one that tests 4 pCi/L in air with 8 pCi/L in the well, because the first has two sources stacking.

Source: EPA drinking water radon guidance (4 pCi/L reference, 10 pCi/L action) and EPA indoor radon program. Figures current as of September 2026.

A note on the top of that table: wells above 100 pCi/L are uncommon in the western US but do occur in uranium-bearing shale and sandstone aquifers. When I have seen 150 pCi/L and higher, the water was also frequently high in other uranium-series parameters, which is why a full panel test matters at that level rather than a radon-only vial.

How to Tell If Your Well Water Has Radon (You Cannot Taste It)

Here is the part that surprises most well owners: there is no visible sign. Radon water looks, smells, and tastes exactly like clean groundwater. It will not stain a tub, discolor a shirt, or leave a film on the glass. The only reliable way to know your level is a test, and the order in which you test matters for both cost and accuracy.

The EPA-recommended sequence starts with an indoor air test, not a water test. That is because the air test captures every source at once: soil gas seeping under the foundation plus radon exhaled from your plumbing. A short-term (2 to 7 day) or long-term (90 day) air canister costs between $20 and $60 and tells you whether your total radon exposure is a problem. If the air test comes back below 4 pCi/L, you are done; your well water is almost certainly not the driver and no water test is needed. If the air test is at or above 4 pCi/L, that is when you pull a water sample to find out what fraction of the problem is coming out of the well.

There are two situations where you skip straight to a water test. First, if you are buying a property with a known elevated radon area and you want a complete picture before closing. Second, if you already know your well draws from a uranium-bearing formation and you want a documented baseline for your treatment decision. In both cases the water test is a lab analysis, not a home kit; the sample must be handled in a way that preserves the dissolved gas, which is where most DIY attempts go wrong.

How to Test for Radon: Indoor Air First, Well Water Second

The two tests use different media and different handling rules, so it is worth understanding each one before you buy a kit.

Indoor air radon test (start here)

Charcoal canisters, electret track-etch detectors, and continuous monitors are all acceptable for an initial screening. For a first look, a short-term charcoal or track-etch kit from a state-certified lab is sufficient and runs $20 to $60 shipped. Place the kit on the lowest lived-in level of the home, at least 20 inches off the floor and away from exterior walls, drafts, and high-heat sources. Keep the windows and doors closed for the exposure period per the kit instructions. The lab reads the canister and reports the result in pCi/L. A 90-day long-term kit smooths out seasonal variation and is the better choice if you are making a treatment decision based on the number.

Well water radon test (second step)

A water radon test is a lab analysis of a sealed sample. You will typically get a glass bottle with a narrow-neck stopper or a specialized radon vial. The handling rules are strict, and breaking them invalidates the sample:

1. Run the tap nearest the well for two to three minutes first, then fill the bottle from that tap. Do not flush a line that has been sitting; you want the water as close to the well as practical, and a short flush removes stagnation bias.
2. Fill the bottle to the brim with no air bubble. Any headspace of air will exchange radon with the surrounding room air during transit and skew the result.
3. Close the stopper tightly and invert the bottle two or three times to mix, per the lab instructions.
4. Label, log the collection time, and ship the sample to the lab the same day it is collected. Radon decays with a 3.8-day half-life, so a sample that sits two days loses roughly 44 percent of its activity before the lab even opens it.
5. Ask the lab to run the sample as total dissolved radon-222 and to report in pCi/L. Some labs also offer radon daughters or a combined uranium-radon panel; ask for the plain radon-222 result first, since that is the number the EPA action level applies to.

Most state health department laboratories, the EPA radon program, and private drinking water labs run this test for between $20 and $60. The state lab is the most reliable choice and is free or low-cost in some states. If your reading comes back at or above 10 pCi/L, ask the lab whether a second confirmatory sample is advisable; a single high reading is worth confirming before you spend on treatment, because well radon can shift with water level and season. For a full breakdown of how to collect every other sample correctly, see our complete well water testing guide.

How to Remove Radon From Well Water: 4 Methods Compared

Once you have confirmed elevated radon in the well, the fix is a mechanical process: you force the dissolved gas out of the water and vent it to the outside air, away from the living space. Four approaches handle the job, and the right one depends on your well depth, your radon level, and your budget. I have installed and serviced all four across private wells, and the ranking below reflects what actually holds up over years of use, not just the brochure claims.

Installed costs reflect 2026 regional pricing for a typical 1-1.5 gpm residential well. Actual quotes vary with well depth, distance from the wellhead to the house, and local labor rates.

Air sparger: the workhorse for private wells

An air sparger is a perforated pipe or stone riser that pushes compressed air up through the well water column. As the air bubbles rise, they sweep dissolved radon out of solution and carry it to the top of the well, where a vent pipe exhausts it outside, away from any air intake or window. For a well in the 4 to 100 pCi/L range, an air sparger with a properly sized compressor and a code-compliant vent is the most common and most cost-effective answer. The two details that make or break it: the compressor must run continuously while the well is in use, and the vent terminal must terminate at least a few feet above grade and well away from the basement supply air. Get the vent placement wrong and you have solved the water problem and created an indoor air problem.

Membrane and air-stripping towers

A membrane or packed-tower stripper takes the same physics and packages it as a dedicated external unit. Water is sprayed or spread over a membrane or packing media while air flows countercurrent, extracting radon with high efficiency. These units handle higher flow and higher starting concentrations better than a simple sparger and are the right call for a large household or a well that tests well above 50 pCi/L. The trade-off is cost and complexity: more piping, a blower or fan, and a vent stack to install. If your quote for a sparger starts approaching the price of a tower, get the tower quote and compare the long-run maintenance.

Activated carbon contactors

An activated carbon contactor pushes the water through a bed of carbon that adsorbs the radon. It is the cheapest option to install and works for low-to-moderate levels, but the carbon saturates and must be replaced on a schedule, and the off-gas from the carbon bed still needs a vent to the outside. For a well at 10 to 20 pCi/L on a tight budget it can be a reasonable stopgap, but for a permanent fix at higher levels the mechanical stripping methods above outperform it on both capacity and lifetime cost. See our radon removal systems buyer guide for model-by-model pricing and the specific units we recommend for each scenario.

Gas release and degassing tanks

A degassing tank uses the pressure drop inside a pressurized vessel to flash dissolved radon out of the water, then vents the gas. It fits naturally into a system that already has a pressurized storage tank, and it is a solid option when the well water arrives with enough pressure to drive the release. The critical engineering detail is the vent: it must be sized for the gas load and routed to the outside, never into a crawl space or attic. For very high-flow households a degassing tank alone may not keep up, in which case pair it with a sparger or tower.

Step-by-Step: From Test Kit to Treated Water

Here is the exact sequence I follow when a well comes up elevated, from the first air canister to a system that holds its numbers year over year. You can do the first three steps yourself; the last two need a licensed contractor.

1. Test indoor air. Run a short-term or long-term radon kit on the lowest lived-in level. Under 4 pCi/L and you stop here; above it, move on.
2. Test the well water. Collect a sealed, no-air-bubble radon sample and send it to a state or EPA-recognized lab the same day. Confirm the result if it reads at or above 10 pCi/L.
3. Know your total budget. Add the air and water numbers in your head. A high air reading with a low water reading points to soil gas (a sub-slab mitigation job, not a water treatment). A high water reading means the well is the source and the fix belongs at the well.
4. Get two to three quotes. For a well-side fix, request quotes from licensed well or radon mitigation contractors. Ask each to specify the method, the compressor or blower size, and exactly where the vent will terminate. A good quote will walk you through the vent path on site.
5. Install and retest. After the system is in, retest both indoor air and well water after 30 days to confirm the drop. Keep the before and after results in your well records; you will want them when you sell the property.

Keeping Radon in Well Water From Coming Back

Radon is not a one-time fix you forget; it is a source you manage. A few habits keep the numbers honest and the system running for the life of the well.

• Retest on a schedule. Recheck the water every one to two years and the indoor air every two years, or after any change in water level, a long dry season, or a change in pump depth. Wells in arid regions can shift radon with the water table, so a dry August can push a 6 pCi/L spring reading toward 9.
• Keep the vent clear. The exhaust terminal should stay free of snow, debris, and bird nests. A blocked vent raises indoor air radon even when the water side is fine.
• Maintain the moving parts. Compressors and blowers have a service life. Replace carbon beds on schedule if you went the contactor route, and keep an eye on any air-bubbling performance drop, which signals a clogged sparger or a tired compressor.
• Document everything. Store every lab report, the install diagram, and the vent location in a single well file. Radon documentation is one of the cleanest selling points on a property with a private well.

Because radon travels with the water table, your well is also a broader health story. If your test panel shows other uranium-series or dissolved solids alongside the radon, the treatment plan can change, so keep the full panel next to the radon result. The same aquifer chemistry that drives radon often drives the other parameters you track, and understanding those interactions is what keeps the whole system stable. For a parallel deep-dive on the other invisible parameter most wells carry, read our guide to manganese in well water, and for the pressure-side companion to these water quality fixes, see how to fix low well water pressure.

Radon in well water is the one contaminant where inaction is the most expensive choice, because the exposure is invisible and cumulative. The good news is that the entire solution is within reach of a private well owner: a $40 air test, a same-day water sample, and a vented stripping system that runs quietly for decades. Test first, treat based on the EPA bands, and get the vent right, and you remove the only radioactive hazard most homes ever face from their drinking water for good.

FAQ: Radon in Well Water

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