If your home runs on a private well, you are the person in charge of your water quality. No utility sends you an annual report, and no agency samples your tap on a schedule. That freedom comes with a to-do list, and radon belongs near the top of it, especially if you live in a part of the country with granite and other bedrock that naturally contains uranium.
Radon is a colorless, odorless gas, so you cannot spot it by looking at a glass of water or smelling the shower steam. The only way to know what is in your well is to test it. This guide walks through how radon ends up in well water, how to collect a sample that gives you a trustworthy result, how to read the lab report, and what to do next depending on the number you get back.
Why Radon Shows Up in Well Water
Radon forms when radium breaks down in soil and rock, and radium itself comes from the slow decay of uranium. Groundwater moves through cracks and pores in bedrock, and as it does, it can pick up dissolved radon gas along the way. A drilled well pulls from those fractures directly, so the water that reaches your home carries whatever it collected underground.
Public systems that draw from large surface reservoirs tend to lose much of their radon before the water reaches a tap, because the gas escapes into the air as water sits and moves. A private well has no such buffer. The water goes from rock to pump to pressure tank to faucet in a short trip, and the gas has little chance to escape on the way.
That is why homeowners in granite regions such as New England are often encouraged to include radon in their routine well testing. Two houses on the same street can see very different results, because the fractures feeding each well are different. Your neighbor’s number tells you something about the area, but it cannot stand in for a test of your own well.
Radon in Water and Radon in Air Are Two Separate Questions
Radon can reach you in two ways. The first is soil gas seeping up through the foundation and into the living space. The second is radon dissolved in your water, which escapes into the air when you run a shower, wash dishes, or do laundry. Those are different sources, and they are measured with different tests.
A water test tells you how much radon is dissolved in the water coming out of your tap, usually reported in picocuries per liter (pCi/L). An air test tells you how much radon is floating in the room, also reported in pCi/L, but in liters of air instead of liters of water. The same unit name appears on both reports, which makes it easy to compare the two numbers by mistake. A water result of 1,000 pCi/L and an air result of 4 pCi/L describe different things and follow different guidelines.
Most of the radon in a typical home comes from the soil beneath it. Water can add to the total, and in homes with a high-radon well it can add quite a bit. Because the two sources combine in the same indoor air, the most complete picture comes from testing both.
Who Should Test Their Well for Radon
If you have a private well and have never had it tested for radon, you are a good candidate. The same goes if your last test was several years ago. Wells can change over time as water tables shift, as nearby construction disturbs the ground, or as a pump is replaced or lowered to a different depth.
A few situations make testing especially worthwhile:
- You are buying a home with a private well and want to know what comes with it.
- You are selling and want results in hand before a buyer asks.
- You have had an air test come back elevated and want to rule water in or out as a contributor.
- You recently had work done on the well, such as a new pump, a deeper pull, or a new pressure tank.
- You live in an area known for granite bedrock and have never looked at your water results beyond bacteria and nitrates.
Homes on municipal water can also have radon in the tap, particularly where a city blends groundwater into its supply. If you are on city water, your supplier’s annual water quality report is the first place to look for that information.
Choosing a Lab and Test Package
Radon in water needs a laboratory analysis. The inexpensive charcoal kits sold for air testing do not measure dissolved radon in water, so look for a certified lab that runs a water-specific radon method. A certified lab follows documented procedures for handling samples, which matters because radon is a gas that can leave the sample if it is mishandled.
Many homeowners find it easiest to work with a local water treatment company that handles sampling and shipping. For example, Absolute Water System in Epping, NH uses an independent laboratory that follows EPA guidelines for water analysis, and its testing packages include radon alongside common well water checks such as arsenic, pH, hardness, iron, manganese, nitrate, and coliform bacteria. Bundling radon with those other parameters gives you a fuller baseline for the same trip to the lab.
If you would rather handle it yourself, call the lab you plan to use and ask for their radon-in-water bottle and written instructions before you collect anything. Each lab has its own container type and its own collection steps, and the lab’s instructions override any general advice you read online, including this article.
How to Collect a Radon Water Sample the Right Way
Because radon is a dissolved gas, the main goal during collection is to keep it dissolved. Anything that adds air or lets gas escape can lower your result and make your well look better than it is. The details vary by lab, but most radon sampling instructions share a few common ideas.
Sample from a tap that sees the whole system
Choose a cold water tap that is located after the pressure tank and before any treatment equipment such as a softener or filter. If you already have a system in place, a sample taken after treatment tells you how well that system is working, while a sample taken before it tells you what the well itself is producing. Many people take both so they can compare.
Run the water, then fill gently
Let the water run for several minutes so you are sampling fresh water from the well and not water that has been sitting in the pipes. Many labs also ask you to remove the faucet aerator, or to use a tube, so the water flows into the bottle in a smooth stream with as little splashing as possible. Splashing and turbulence let radon escape into the air.
Fill the bottle completely and seal it
Most labs want the bottle filled to overflowing and capped with no air bubbles trapped inside. Tilt the bottle, fill it slowly, and cap it underwater or while the water is brimming at the top, depending on the lab’s directions. Then label it with your name, the date, and the exact time of collection.
Get it to the lab quickly
Radon decays on a short timeline, which is one reason labs set tight deadlines for delivery after sampling. Ask the lab how soon the bottle needs to arrive, collect your sample on a day when you can drop it off or ship it right away, and avoid collecting right before a weekend or holiday when the package might sit in transit.
Do an Air Test Too
A water test answers one question. An air test answers the question that matters most for your health, which is how much radon you are actually breathing at home. If you are testing your well, consider testing the air in the lowest lived-in level of the house at the same time.
Short-term air kits run for a few days, and long-term kits run for months. Short-term tests give a quick snapshot, and long-term tests smooth out the daily swings caused by weather, ventilation, and season. Place the kit away from drafts, windows, and exterior walls, and keep doors and windows closed as the kit directions describe.
If the air result comes back high and the water result is also high, you have two sources to address. If the air is high and the water is low, soil gas is likely the main source and a sub-slab system or similar air-side fix is the better path. If the air is acceptable and the water is high, your well may still deserve attention, because water use can raise indoor air levels during heavy-use times of day, and that is not always captured by a single air test.
How Long Results Take
Turnaround depends on the lab. When Absolute Water System collects and submits samples through its independent lab, results typically come back within five days. If you work with a lab directly, ask for their turnaround time when you request the bottle so you know when to expect the report.
When the results arrive, you will usually receive a PDF or printed report listing each parameter tested, the measured value, the unit, and a reference level or reporting limit. Keep a copy in the same folder as your well records, such as the drilling log, pump information, and past test reports. A history of results makes it much easier to spot a trend later.
How to Read Your Radon Water Result
Start with the unit. Radon in water is generally reported in pCi/L. Find the line labeled radon and note the number next to it. Then look at the reference level the lab lists, if there is one. Reference levels vary because different agencies set different guidance values, so the lab’s comparison column is a starting point and not the full story.
Here is a practical way to think about it:
- Very low or non-detect: Your well is not contributing meaningful radon at the time of sampling. Retest on a regular schedule, since conditions can change.
- Low but detectable: Radon is present, and the amount may be manageable with a point-of-entry carbon filter or may need no action at all, depending on the number and your air results.
- Elevated: The amount is high enough that treatment is worth discussing. An aeration system is commonly recommended for higher levels.
For airborne radon, the EPA recommends fixing a home when one long-term test, or the average of two short-term tests, shows 4 pCi/L or higher, and it suggests considering a fix when levels fall between 2 and 4 pCi/L. Those air numbers are the benchmark most homeowners hear about. Your state environmental agency also publishes guidance on radon in private well water, and it is worth reading before you decide what level of reduction you want to aim for.
What to Do If Your Result Is Low
A low result is good news, and it still earns a place in your records. Write down the date, the lab, the sample location, and whether the sample was taken before or after any treatment. Then set a reminder to retest. Many water professionals suggest testing private wells for radon about every two years, and sooner if you notice changes in the water or make changes to the well.
If your result is low but detectable, think about how your household uses water. Long hot showers in a small bathroom with poor ventilation release more dissolved gas into the air than a quick rinse at the kitchen sink. Running the bathroom exhaust fan during and after showers is a simple habit that helps with radon along with moisture and odors.
What to Do If Your Result Is High
An elevated result is a common finding in granite regions, and there are well-established ways to deal with it. The two main approaches are carbon filtration and aeration, and the right choice depends on how much radon is in the water and how much water your household uses.
Granular activated carbon
A down-flow carbon filter can handle lower radon levels. The carbon traps radon as water passes through the tank. It works well within its range, though the media needs to be replaced on a schedule and the filter should be tested periodically. One thing to keep in mind is that carbon can build up radioactivity over time as it collects radon decay products, so the tank location and the disposal of used media deserve a conversation with your installer.
Aeration systems
For higher radon levels, an aeration system is generally the stronger option. In these systems, water flows into a storage tank where air is bubbled up through it, which pulls the radon out of the water and vents it safely outdoors. If you are weighing options, a radon water mitigation system built around aeration is usually what installers recommend when numbers are well above the low range, because it removes radon from the water instead of storing it in a filter bed.
Match the system to the whole water profile
Radon rarely shows up alone. The same bedrock that releases radon can also contribute arsenic, iron, manganese, or acidity, and each of those influences which equipment makes sense and in what order. A system sized and laid out for your complete lab report will work better than one chosen from the radon result alone, which is a good reason to test for the full set at the start.
Retest After Treatment
Installing a system is the middle of the process, not the end. Once it has been running for a little while, collect a sample after the treatment equipment and send it to the lab to confirm that radon is being reduced. Follow it with an air test so you can see how indoor levels responded.
After that, a routine schedule keeps the system honest. Filters and media need replacement, blowers and pumps need servicing, and water chemistry can drift. A short service visit and a follow-up test every couple of years are far cheaper than discovering a problem after a long period of reduced performance.
Testing During a Home Purchase
If you are buying a house with a private well, a radon water test fits right alongside the standard inspection items. Ask your inspector or water treatment company to add radon to the well water sampling, and build the lab turnaround into your timeline so results arrive before your decision deadlines.
A high radon result does not have to end a purchase. It is a known, fixable condition, and having the number early lets you ask the seller about a credit or plan the installation as part of your move-in budget. Buyers who know their results are in a much better position than those who learn about radon after closing.
Why Local Knowledge Helps
Radon levels and the other contaminants found in well water vary from region to region, so a professional who works in your area can tell you what is typical for local bedrock and which combinations they see most often. For anyone searching for New Hampshire water testing, that local context is worth asking about, because it shapes which parameters should go on the order form and how to interpret the report that comes back.
Whoever you work with, look for clear communication. A good provider will explain the numbers in plain language, tell you what each result means for your household, and give you options at different price points when treatment is called for. If you do not understand a line on your report, ask for a walkthrough before you decide on anything.
Common Mistakes That Skew Radon Results
Most problems with radon water tests come from a handful of simple errors, all of which are easy to avoid once you know about them:
- Sampling from a hot tap. Heating drives gas out of water, so use the cold line.
- Collecting from an aerated faucet. Bubbles and splashing release radon before it reaches the bottle.
- Leaving air in the bottle. A headspace gives the radon a place to go.
- Waiting too long to ship. Radon decays quickly, so delays can lower the measured value.
- Mixing up the units. Water and air results share the pCi/L label but follow different guidelines.
- Testing once and forgetting. One result is a snapshot, and repeat tests show whether anything is changing.
A Simple Plan for the Next Month
If radon testing has been sitting on your list, you can finish the first round in a few weeks. Start by calling a certified lab or a local water treatment company and asking for a package that includes radon. Collect the sample using the lab’s instructions, and get it to the lab right away. While you wait for results, place an air test kit in the lowest lived-in level of the house.
When the reports come back, put the water and air numbers side by side, file the paperwork, and decide whether the results call for action or a reminder to retest in a couple of years. Either outcome gives you something valuable: certainty about what is flowing through your home. With a private well, that certainty is the foundation for every other decision about your water.
