How Does Radon Get Into Well Water, and How Do You Reduce It in Your Home?
Radon is one of those household topics that tends to surface at an awkward moment: during a home inspection, after a neighbor’s test comes back high, or when a water report lands in your inbox with a line you have never seen before. If you rely on a private well, the question that follows is usually the same. How does a radioactive gas end up in the water coming out of your tap?
The short version is that radon starts in the ground and water carries it along. The longer version is worth understanding, because it explains why testing matters, why there are two separate routes into a house, and why the fixes for each route look so different. This guide walks through the whole path, from bedrock to bathroom, and then covers practical ways to bring radon down once you know it is there.
Where Radon Comes From in the First Place
Radon is a naturally occurring gas that forms when uranium in rock and soil slowly breaks down. Uranium is present in small amounts in many kinds of bedrock, and as it decays it produces radium, which in turn decays into radon. Radon has no color, smell, or taste, so there is no way to notice it without testing.
Because the source is geology, radon levels vary from one region to the next and even from one property to the next. Two houses on the same street can sit on very different rock and soil, and they can show very different results. That is why a neighbor’s test is interesting but never a substitute for your own.
Granite and certain other crystalline rocks tend to contain more uranium than many sedimentary rocks. New England sits on a lot of this kind of bedrock, which is a big reason radon testing is a regular part of buying or owning a home in the region.
How Radon Dissolves Into Groundwater
Rain and snowmelt soak into the ground and move slowly through soil and cracks in the rock. That moving water is groundwater, and it is what a private well draws from. While it travels through fractures in the bedrock, it comes into contact with rock that is continuously releasing radon gas.
Gas dissolves in water, much like the carbon dioxide in a bottle of sparkling water. The longer groundwater stays in contact with radon-producing rock, and the more of that rock it touches, the more radon it can pick up. Deep bedrock wells often draw from water that has spent a long time in these fractures, so they can carry more dissolved radon than a shallow well or a surface supply.
The important detail is that radon stays dissolved as long as the water is underground and under pressure. Nothing visible changes in the water. It looks clear, tastes normal, and can pass every sensory check you have.
Why Private Wells Are Affected More Than City Water
Municipal systems usually draw from large reservoirs or surface sources, and they handle water in open tanks and long pipe runs before it reaches your tap. Radon is a gas, so it tends to escape from water that is exposed to the air for a while. By the time city water arrives at a house, much of any radon has already left it.
A private well is different. Water moves from the rock to the well and then straight into your plumbing, with very little time in open air. The radon that dissolved underground arrives at your faucet largely intact. For that reason, radon in water is mainly a private well question, and it deserves a place on the list next to bacteria, arsenic, and other common groundwater tests.
What Happens Inside the House When You Use Water
Once radon-bearing water enters the house, ordinary daily activities release the gas into the air. Hot showers are the classic example, since warm, agitated water lets dissolved gas escape quickly into a small, enclosed bathroom. Running a washing machine or dishwasher, filling a tub, and even running a kitchen tap do the same thing on a smaller scale.
That is the core reason radon in water matters. Most of the exposure from water comes from breathing the gas that leaves it, not from drinking it. A bathroom with the door closed and the fan off can hold a noticeable amount of released radon during and after a shower, and that gas then drifts through the rest of the home.
Water is only one contributor to the radon you breathe indoors. In most homes, the larger share comes from the soil gas that enters through the foundation, which brings us to the second route.
The Other Route: Soil Gas Under Your Foundation
Radon in the ground does not only dissolve in groundwater. It also moves as a gas through soil and rock, and a house acts a bit like a chimney. Warm air rises and leaves through the upper levels, which lowers the air pressure at the bottom of the house slightly, and that gentle suction pulls soil gas in through any opening it can find.
Typical entry points include cracks in a concrete slab, gaps around pipes and sump pits, the joint where the floor meets the wall, and uncovered dirt in a crawl space. A well-sealed foundation helps, but sealing alone rarely solves the problem, because gas finds the smallest gaps and the pressure difference remains.
This matters for well owners because the two routes can both be present. A home can have radon in its water, radon in its soil gas, or both, and the right fix depends on which source is driving the result. Treating only one of them can leave the other untouched.
Why Radon Exposure Deserves Attention
Radon is radioactive, and breathing it over many years is recognized by health agencies, including the US EPA, as a cause of lung cancer. The risk builds up gradually through long-term exposure, so a single high reading is not an emergency, but it is a reason to act sensibly and without long delays.
For indoor air, the EPA uses an action level of 4 picocuries per liter and encourages homeowners to consider fixing a home at that level. It also notes that there is no known completely safe level, so lower results are better than higher ones. For water, the goal is simply to bring radon down enough that showering and daily use no longer add meaningfully to what is in your indoor air.
There is no reason to be alarmed. Radon is common, well understood, and very fixable. The steps below take most homeowners from “I have a number I do not like” to a confident, measurable solution.
Testing: The Step That Makes Everything Else Easier
Because radon cannot be seen or smelled, testing is where every good plan begins, and for a well owner it takes two forms.
An air test measures the radon in the living space. Short-term kits are inexpensive and widely available, and a longer test gives a better picture of your typical level across changing weather and heating seasons. Place the kit in the lowest lived-in level of the home and follow the instructions closely, since closed windows and steady conditions matter for accuracy.
A water test measures the radon dissolved in your well water. This needs a proper sample collected the way the lab specifies, because radon escapes easily if water sits open or is handled carelessly. A professional who offers water testing will usually collect the sample correctly and send it to a lab that handles radon analysis. Testing air and water together tells you which route is contributing and how much, and that is the information that shapes your solution.
Two Main Ways to Remove Radon From Well Water
Once a water test confirms radon, there are two established treatment approaches. Each one suits different conditions, so it helps to understand both.
The first is granular activated carbon. Water passes through a tank of carbon that captures radon. It can work well at lower concentrations, but the carbon itself collects radioactive decay products over time, which creates handling and disposal considerations. Carbon systems also tend to lose effectiveness at higher radon levels.
The second is aeration, which does the opposite of capturing the gas. It encourages radon to leave the water, then vents it safely outdoors. Because radon is a gas that escapes readily, aeration is typically the preferred choice for higher concentrations and is widely used for private wells in radon-prone regions.
How Aeration Systems Work
An aeration system brings water into contact with a large volume of air. Water enters a sealed tank, where a blower moves air through it or breaks the water into fine droplets, giving dissolved radon the chance to move from the water into the air. The radon-laden air is then vented outside, away from windows and living areas, and the treated water is pumped on to your plumbing.
One example of this design is the AcceL-AerAtor E99, which the Epping, NH team at Absolute Water System describes as over 99 percent efficient at removing radon from water. It is a self-contained unit that plugs into a standard outlet, and the manufacturer designed it so that the whole unit can be opened for cleaning without special tools. If you are comparing water aeration systems New Hampshire homeowners rely on, details like these are worth lining up side by side: how much of the radon the unit removes, how it handles power interruptions, what alarms it provides, and how simple cleaning is.
Aeration does one thing particularly well. It takes the radon out of the water before it reaches your faucets, so showers, laundry, and dishwashing no longer release it into the house. That is the direct fix for the water route, and it protects every tap rather than only the kitchen sink.
Why a Point-of-Use Filter Is Not Enough
It is tempting to think a small filter at the kitchen tap could deal with radon. Radon in household water mostly matters when it escapes into the air, and that happens at every shower and appliance in the house. A filter at a single faucet leaves the rest of the plumbing untouched.
Whole-house treatment at the point where water enters the home addresses the full supply. This is also why a treatment plan should start from your test results rather than from a product, since the radon concentration, flow rate, and household size all shape what size of system makes sense.
Reducing Radon in the Air: Sub-Slab Venting
If your air test is high, the fix targets the soil gas. The standard approach is a sub-slab depressurization system. A pipe is placed through the foundation slab into the gravel or soil below, and a fan draws radon from under the floor and pushes it through a vent pipe to a point above the roof or outside, where it disperses harmlessly in open air.
The fan is a low-wattage device, similar to a bathroom fan but quiet, and a well-installed system needs very little maintenance. Placement of the fan matters. It belongs outside, in an attic, or in an unfinished garage, and not inside the finished living space of the house, because a frozen or blocked vent could otherwise push radon back into the home.
You may hear that a passive vent pipe with no fan is enough. Without the fan, there is no negative pressure under the slab to draw gas out, so passive systems do not perform reliably. The cost difference between a passive and an active system is small, and the active system is the one that actually works. This is a good job for radon air purification specialists who understand foundations, pipe routing, and fan placement.
When a Home Needs Both Fixes
Some homes have a mild air result and a high water result, others the reverse, and plenty have elevated numbers in both. When both routes contribute, treating them together gives the best outcome, and retesting after installation shows whether each fix did its job.
A sensible order is to test the water and the air, treat the larger source first, and then retest. If the air number is still above where you want it after the water system is running, the soil gas route may need its own system. Working in sequence with real numbers avoids paying for equipment you do not need and gives you proof that the work is paying off.
Good Questions to Ask Before Hiring an Installer
Radon systems involve plumbing, electrical power, and venting, so it helps to work with a company that handles all three. A few questions make comparisons easier.
- Will the design be based on my own water test results and my home’s layout?
- Where will the system vent, and how will the vent be protected from freezing or blockage?
- What alarms or notifications will tell me if something stops working?
- What does routine maintenance involve, and who performs it?
- What warranty covers parts and labor?
Answers to these tell you a lot about how the installer works. A company that designs around the actual water in your home, rather than offering one standard package, is usually the better fit, because radon rarely appears alone. Wells that carry radon often carry other things worth checking at the same time, such as iron, manganese, arsenic, or low pH, and a good design accounts for those.
Caring for the System After It Is Installed
Aeration units benefit from periodic inspection and cleaning, since minerals in the water can build up inside the tank and on internal parts over time. The manufacturer’s guidance sets the schedule, and a unit that is easy to open and clean makes that chore simpler. Keep the alarm functional, and take note if it ever sounds.
Air systems need little more than an occasional look at the fan and the pressure indicator, which many installers include on the pipe so you can see at a glance that the fan is running. Retesting every couple of years, and after major changes such as foundation work or renovations, keeps your picture current.
It also helps to keep your test results and installation paperwork together. If you ever sell the home, a documented before-and-after record answers buyer questions quickly and shows the issue was handled properly.
Putting It All Together
Radon gets into well water because groundwater travels through rock that continuously releases radon, and the gas dissolves in the water and rides along to your tap. It gets into the house air through a second route, soil gas drawn in through the foundation. Testing tells you which route matters in your home, aeration is a proven answer for radon in water, and fan-driven sub-slab venting is the standard answer for radon in air.
If your results point to a system, getting the right equipment sized and set up correctly is worth the attention it takes. When you are ready to move from numbers to a working solution, you can schedule a home water system installation today with a team that designs each system around the home’s actual water, then retest to confirm the result. A calm, step-by-step approach turns radon from an unknown into a managed part of owning a home on well water.