Radon in Water Test Kit: What Homeowners Need to Know
Most homeowners think of radon as an air problem, but well water can carry dissolved radon straight into the house, releasing it into the air every time someone showers, runs the dishwasher, or fills a sink. A radon in water test kit measures that dissolved gas so you can tell whether your private well is adding to your indoor exposure. Homes on public water rarely need this test, but those on private wells in radon-prone regions do. This guide summarizes EPA and CDPHE guidance current as of 2026; it is educational and not a substitute for a certified laboratory analysis or medical advice from your physician.
What a Radon in Water Test Kit Measures
A radon in water test kit captures a water sample and sends it to a laboratory that measures dissolved radon, reported in picocuries per liter (pCi/L) of water. This is a different measurement from an airborne radon test, which reports radon in air. The two are related but separate problems, and a complete picture often requires testing both.
The mechanism behind waterborne radon is straightforward. Groundwater moving through uranium-bearing rock picks up radon. When that water reaches the tap and is agitated, the gas escapes into the indoor air. Roughly speaking, the EPA estimates that 10,000 pCi/L of radon in water contributes about 1 pCi/L to indoor air, though local ventilation changes the ratio. For the broader context of why radon matters in this region, see our hub on radon testing for Colorado homeowners.
The activities that release the most waterborne radon are the ones that agitate and heat water: showering, running the washing machine, and operating the dishwasher. Bathrooms and laundry rooms therefore tend to show the highest momentary air concentrations from a water source, which is why ventilation in those rooms matters alongside any treatment.
Who Actually Needs to Test Water for Radon
This test is for private well owners, not households on municipal supply. Public water systems treat and aerate water in ways that strip out most dissolved radon before it reaches homes, and they are regulated and monitored. Private wells receive no such treatment, so the gas travels directly from the aquifer to the tap.
The risk rises sharply in areas with uranium-rich bedrock, which includes parts of the Colorado Front Range and mountain communities. If your air test came back elevated, it is also worth checking whether well water is a contributing source, since fixing only the air leaves part of the problem in place. Our broader piece on radon in water and how it enters homes covers the geology in more detail.
Households drawing from a shared or community well in a high-radon area should also consider testing, since these smaller systems may not aerate water the way large municipal plants do. When in doubt about your water source, your county health department can tell you whether your supply is regulated.
How to Use a Radon in Water Test Kit
Waterborne radon escapes quickly when water is agitated, so sampling technique is critical. The kit instructions are designed to prevent that loss, and skipping steps produces falsely low results.
- Collect the sample from a tap close to where water enters the home, before any treatment system.
- Run the cold water briefly to clear standing water, then reduce flow to a gentle stream.
- Fill the vial completely with no air bubbles, submerging the bottle if the kit directs you to.
- Cap it immediately underwater or with minimal splashing to trap the radon.
- Mail it to the lab the same day, since radon decays with a short half-life.
The same-day shipping rule is non-negotiable. Radon-222 has a half-life of about 3.8 days, so a sample that sits for a week loses much of its measurable radon and understates the true level. Some labs build the decay time into their calculations, but only if you record the exact sampling date and time on the form, so fill that out carefully.
Understanding Your Results
The EPA has not finalized a single enforceable standard for radon in water, but it has proposed reference levels. The widely cited proposed maximum contaminant level is 300 pCi/L where the state runs a multimedia program to reduce radon in air, and an alternative level of 4,000 pCi/L where it does not. Many labs flag results above these benchmarks.
Because the air-to-water relationship is roughly 10,000-to-1, a water result of 4,000 pCi/L adds only a fraction of a picocurie to indoor air. The practical takeaway: very high water numbers can still translate to modest air contributions, but they compound any radon already entering through the soil. Reading these figures alongside an air test, using a resource like our radon level chart, gives the clearest picture of total exposure.
Air vs. Water Radon: Why You May Need Both Tests
Soil gas is the dominant source of indoor radon for most homes, entering through foundation cracks and sump pits. Water is a secondary contributor, significant mainly for private-well households. Testing only the water while ignoring the air, or vice versa, can leave a major exposure path unmeasured.
The sensible sequence for well owners is to run an air test first, and if it is elevated, follow with a water test to determine how much the well contributes. That ordering keeps costs reasonable while still catching the most common source. If the air test is high but the water test is low, the problem is in the soil and a standard mitigation system is the answer; if both are high, you may need to address both pathways.
How to Reduce Radon in Water
If a water test comes back high, two proven treatment methods exist, and both are installed at the point where water enters the home, treating all the water before it reaches any fixture.
Aeration Systems
Aeration bubbles air through the water to release radon, which is then vented outdoors. The EPA generally considers aeration the preferred method because it does not concentrate radioactivity and handles high levels effectively. Aeration systems cost more upfront and require some maintenance, but they avoid the disposal concerns of carbon filters.
Granular Activated Carbon (GAC)
GAC filters adsorb radon as water passes through a carbon bed. They work well for lower concentrations and cost less to install, but the carbon accumulates radioactivity over time and requires careful handling and eventual disposal. Our guide to a radon water mitigation system compares both approaches in depth, including when each is the better fit.
Retesting After Treatment
Installing a treatment system is not the end of the process. A follow-up water test confirms the system actually reduced radon to a safe level, and periodic retesting verifies it keeps performing as the media ages or the aeration components wear. For GAC systems especially, the carbon’s capacity declines over time, so a maintenance and retesting schedule protects against silent failure.
How a Water Result Translates to Air Risk
The number a water test returns can feel hard to interpret on its own, so it helps to connect it to air. The EPA’s working ratio is roughly 10,000 pCi/L in water contributing about 1 pCi/L to indoor air. A well at 10,000 pCi/L, then, adds about a full picocurie to the home’s air, which is significant when stacked on top of soil-gas radon already present.
This ratio is approximate because it depends on how much water the household uses and how well the home ventilates, but it gives a useful rule of thumb. It also clarifies why water rarely accounts for an entire elevated air reading: reaching 4 pCi/L from water alone would require an extraordinarily high water concentration. In most affected homes, water is a contributor that pushes an already-elevated soil reading higher, which is exactly why measuring both pathways gives the truest picture of total exposure and the right basis for choosing a fix.
How Radon Gets Into Groundwater
The path from rock to tap explains why some wells are affected and others are not. Radon forms continuously as uranium and radium decay in the bedrock and soil. Where groundwater flows through uranium-rich granite or fractured rock, it dissolves radon along the way. By the time that water reaches a well intake, it can carry a substantial dissolved radon load straight into the home’s plumbing.
Surface water, by contrast, loses most of its radon to the open air before it is ever collected, which is one reason municipal systems drawing from reservoirs rarely pose a waterborne radon problem. Wells drawing from deep bedrock aquifers in radon-prone geology are the classic high-risk case. Because the Front Range and Colorado mountain communities sit on exactly that kind of rock, private-well owners there have a real reason to consider a water test alongside their air test.
Symptoms of a Waterborne Radon Problem
Waterborne radon produces no taste, color, or odor, just like airborne radon, so there are no sensory warning signs. What homeowners can sometimes infer is a pattern: an air test that reads higher than the home’s foundation and soil conditions alone would predict, especially in bathrooms and laundry areas, can hint that water is contributing. The only way to confirm it, though, is a dedicated water test.
This is why well owners with an elevated air result should not assume the soil is the whole story. A modest soil contribution plus a meaningful water contribution can add up to a reading that a soil-only mitigation system will not fully resolve. Measuring both pathways prevents the frustration of installing a system that only partly fixes the problem.
Comparing the Two Treatment Methods
When a water test confirms a problem, the choice between aeration and granular activated carbon comes down to the concentration and the homeowner’s priorities. Aeration handles very high levels, vents the radon safely outdoors, and avoids concentrating radioactivity, but it costs more and includes a tank, blower, and venting that require space and maintenance.
Granular activated carbon is simpler and cheaper to install and suits lower concentrations well. Its drawback is that the carbon bed accumulates radioactivity over time, which raises handling and disposal considerations and, at high radon levels, can become significant enough that aeration is preferred. A water-treatment professional sizes the system to your measured level, which is the practical reason to test before buying any equipment. Oversizing wastes money, while undersizing leaves radon in the water, so the measured number is what anchors a sensible purchase. Either system is installed where water enters the home, treating the whole supply before it reaches any tap or shower, which is the only placement that addresses every fixture at once.
When to Call a Professional
Bring in a certified radon professional or a licensed water-treatment specialist when your water test comes back high, when you are unsure whether your air problem stems from soil or water, or when you are buying a home served by a private well. A professional can test both media, size the right treatment system, and verify performance after installation. For well owners on the Front Range, that combined approach prevents paying for the wrong fix and ensures the whole exposure path is addressed.
References
- Radon in Drinking Water — U.S. Environmental Protection Agency
- Radon Information for Colorado Residents — Colorado Department of Public Health and Environment
- Radon and Your Health — American Lung Association
Front Range well owners who want both air and water radon checked before relying on a private supply can reach a vetted local inspector through our contact page.
Radon test kits we recommend
Short-term charcoal kits are the cheapest way to get a first reading; mail the canister to the lab and results come back in days.
| Product | Why | Buy |
|---|---|---|
 AirChek Charcoal Radon Test Kit | Lab fee usually included; EPA short-term protocol. | Amazon — $21.95 |
 First Alert RD1 Radon Test Kit | Widely stocked; 48-hour charcoal test. | Amazon — $17.95 |
| Health Metric Radon Test Kit | Two-pack option for closed-house testing. | Amazon — $17.95 |