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Radon is a radioactive gas that seeps out of certain bedrock and dissolves into well water, and unlike most contaminants on this site, the biggest health risk is not drinking it but inhaling it as it off-gasses during a hot shower. Standard filters barely touch it. This guide explains why, which two technologies actually work, and which products give a household a realistic, verified reduction.
Table of Contents
Quick Answer
The key point: Radon dissolved in well water needs aeration or granular activated carbon, not a standard filter, pitcher, or reverse osmosis system, none of which reliably strip a dissolved gas out of solution. The RadonAway RMW-15 is our top pick as a purpose-built spray aeration system that reaches roughly 99 percent removal, with a Fleck 5600 SXT catalytic carbon system as a runner-up for moderate levels where a smaller footprint matters more than maximum reduction.
What Is Radon, and Why Does It Show Up in Well Water
Radon is a colorless, odorless, radioactive gas produced by the natural decay of uranium and radium in rock and soil. It is best known as an indoor air problem that seeps up through foundations, but the same gas also dissolves into groundwater as it moves through uranium-bearing bedrock like granite, shale, and some metamorphic formations. Because municipal surface water sources like rivers and reservoirs are exposed to open air, most of their dissolved radon off-gasses naturally before it ever reaches a treatment plant. Private wells drilled into radon-bearing bedrock do not get that benefit, which is why radon in drinking water is overwhelmingly a well-water issue rather than something municipal customers need to worry about.
The health risk works differently than with most contaminants in our water contaminant database. The EPA's primary concern with radon in water is inhalation, not ingestion: every time radon-laden water is agitated, whether in a shower, a washing machine, or a dishwasher, a portion of the dissolved gas releases into the air, and breathing it in over years is linked to an elevated lung cancer risk on top of whatever risk comes from radon that has already seeped into the home through the foundation. A smaller, secondary risk comes from actually swallowing the water, which the EPA associates with a modest increase in stomach cancer risk. Geographic risk varies enormously by region; states with significant granite or shale bedrock, including parts of New England, the Appalachians, the Upper Midwest, and the Mountain West, see the highest well-water radon levels, but any private well can test high regardless of what a neighbor's well shows, since radon concentration depends on the specific rock a well is drilled into.
How Radon in Water Is Regulated
Radon in drinking water sits in an unusual regulatory gap. The EPA proposed a federal standard back in 1999 that would have set an Alternative Maximum Contaminant Level of 4,000 picocuries per liter for utilities that also run an active indoor radon-reduction program, or a stricter 300 picocuries per liter limit for those that do not, but that proposal was never finalized into an enforceable rule. Decades later, there is still no federal Maximum Contaminant Level specifically for radon in water, which puts it in a similar regulatory limbo to several other contaminants covered in our EPA drinking water standards guide.
In practice, a handful of states with widespread radon-bearing bedrock have stepped in with their own guidance or action levels. New Hampshire, Maine, and New Jersey are among the most active, publishing recommended action levels for private well water that most falls somewhere between 4,000 and 10,000 picocuries per liter, though the exact number and whether it is enforceable or advisory varies by state. If your state has not published specific guidance, the non-binding EPA proposal levels are a reasonable reference point, but because radon is a known human carcinogen with no safe threshold, many public health officials recommend treating any well that tests above roughly 4,000 pCi/L, and seriously considering treatment above 10,000 pCi/L regardless of what your specific state requires.
Which Treatment Technologies Actually Reduce Radon
This is a contaminant where the standard advice for most of our other guides, reach for reverse osmosis, does not apply. Radon is a dissolved noble gas, not a dissolved solid or a larger organic molecule, and RO membranes are built to reject ions and larger compounds, not small, non-polar gas molecules that pass through in solution much like the water itself. Standard carbon pitchers, faucet filters, and refrigerator filters are sized and designed for chlorine taste and larger organics, and none of them provide meaningful contact time or media volume to strip a gas out of water. If a product's marketing does not specifically claim NSF/ANSI testing for radon reduction, assume it does nothing for this particular contaminant.
Aeration is the technology municipal engineers and radon-mitigation contractors consider the gold standard, and it works on a simple principle: radon is far more soluble in water than it wants to be, so aggressively mixing air into the water drives the dissolved gas back out of solution before it ever reaches a tap. Spray aeration systems, which pump water through a fine spray head inside a vented tank, and packed tower aeration, which trickles water down through a column of media while air is blown upward through it, both routinely achieve 95 to over 99 percent radon removal when sized and vented correctly. The trade-off is that aeration systems need mechanical parts (a blower or spray pump), a vented tank, and a repressurization pump to restore water pressure afterward, which adds equipment, some maintenance, and upfront cost compared to a simpler cartridge filter.
Granular activated carbon, specifically whole-house point-of-entry tanks like the ones covered in our best whole-house water filters roundup, is the other proven option, and it works differently: rather than releasing the gas, GAC media adsorbs radon onto its surface as water passes through a large-volume tank. GAC is simpler, has no moving parts beyond a standard backwashing valve, and costs less upfront than aeration, but it has two real limitations. First, it is generally recommended only for low-to-moderate radon levels, since very high concentrations need more contact time and carbon volume than most residential tanks provide. Second, and more unusual, the carbon bed itself becomes measurably radioactive over time as it accumulates radon and its decay products, which means some states require gamma radiation shielding or professional disposal of spent GAC media, a consideration that does not come up with any other contaminant on this site. Softeners, sediment filters, and UV disinfection systems have no meaningful effect on radon at all.
Best Radon-in-Water Treatment Products
| Product | Technology | Typical Removal | Price | Best For |
|---|---|---|---|---|
| RadonAway RMW-15 | Spray aeration, whole-house | ~99% | $1,400+ | Best overall, moderate to high radon |
| Fleck 5600 SXT catalytic carbon system | Whole-house GAC/catalytic carbon | ~80-90% at moderate levels | $900-$1,300 | Lower levels, smaller footprint |
| AccuStar Radon in Water Test Kit | Certified lab test, not treatment | N/A (diagnostic) | ~$40 | Confirming your level before buying equipment |
RadonAway RMW-15 (best overall): RadonAway built its reputation on indoor air radon mitigation, and the RMW-15 applies the same expertise to water, using a compact spray aeration tank with an integrated blower and automatic controls sized for typical residential well flow rates. It is designed and tested specifically for radon reduction, routinely reaching removal rates near 99 percent even at higher starting concentrations, which makes it the system radon-mitigation contractors reach for first when a well tests high. Check current pricing and availability. The trade-offs are real: it needs a dedicated vent to the outdoors, a repressurization pump, more installation space than a filter cartridge, and periodic blower maintenance, so most households have it professionally installed rather than doing it themselves.
Fleck 5600 SXT catalytic carbon system (runner-up): For wells testing at more moderate levels, a backwashing whole-house tank built around the workhorse Fleck 5600 SXT valve and filled with catalytic carbon media offers real radon adsorption without the vent, blower, and repressurization equipment aeration requires. It is simpler to install, takes up less mechanical room space, and doubles as general chlorine and taste/odor reduction for the rest of the house. The catch is the ceiling: it is not the right choice for a well testing well above moderate action levels, and the accumulated radioactivity in spent media means it should be swapped out and disposed of on the schedule your supplier recommends, not left in service indefinitely to save money.
AccuStar Radon in Water Test Kit (start here): Before buying either system, confirm you actually have a radon problem and roughly how severe it is. AccuStar is one of the most widely used names in radon testing and its water kit uses a sealed sample vial specifically designed to prevent the gas from escaping before the lab can measure it, which matters because a loosely capped jar will read artificially low. See current listings. At roughly the cost of a nice dinner out, it is the cheapest way to avoid either overpaying for aeration you do not need or underinvesting in a GAC tank that cannot handle your actual level.
How to Test for Radon in Your Water
Radon has no taste, odor, or color, so there is no way to detect it without a test, and unlike an indoor-air radon test you can run yourself with a basic detector, a reliable water test requires a certified laboratory and a specific collection method. The sample must be drawn directly from an untreated tap as close to the well as possible, filling the vial completely with no air bubbles and sealing it immediately, because any agitation or exposure to air lets dissolved radon start escaping before the lab ever sees the sample. This is different from most other contaminant tests on this site, where a standard sample jar and a few days in the mail cause no meaningful measurement drift; radon sampling error is almost always caused by improper collection, not lab error. Our how to test your water quality guide covers general sampling best practices, and our best water test kits roundup is a useful reference if you want to compare radon-specific kits against general contaminant panels.
Because radon levels in the same aquifer can vary somewhat over time and even seasonally, a single test is a reasonable starting point, but a well testing close to your state's action level is worth retesting before making a final equipment decision, and definitely worth retesting after installing any treatment system to confirm you are actually getting the reduction the manufacturer claims. If you are also dealing with other private-well concerns identified during testing, our well water filtration guide covers how radon treatment fits alongside iron, hardness, and bacteria concerns that often show up on the same property.
Aeration or GAC: Which Fits Your Situation
The honest answer depends almost entirely on your tested radon level and how much installation complexity you are willing to take on. If your well tests well above your state's action level, or if your state does not publish a specific number and your result is in the tens of thousands of picocuries per liter, aeration is the technology with the track record to get you into a genuinely safe range, and the added equipment and professional installation cost is the price of actually solving the problem rather than partially treating it. If your level is closer to the low end of your state's action range, a whole-house GAC or catalytic carbon tank is a reasonable, lower-cost, lower-maintenance option that still meaningfully cuts your exposure, provided you commit to replacing the media on schedule rather than treating it as a install-and-forget system the way you might with a sediment filter.
Either way, treatment should happen at the point of entry to the whole house, not at a single kitchen tap, since the inhalation risk that concerns the EPA most comes from showers and other water uses throughout the home, not just from drinking water. A single under-sink filter, no matter how good, only protects the water coming out of one faucet and does nothing for the shower down the hall. If a radon test also turns up other well-water issues, treating them together during the same plumbing project is almost always cheaper than running separate systems installed at different times.
Frequently Asked Questions
No, not meaningfully. RO membranes are built to reject dissolved solids and larger molecules, but radon is a small, non-polar dissolved gas that passes through a standard RO membrane along with the water itself. Aeration or granular activated carbon are the only treatment technologies with a proven track record against radon.
Almost never. Radon in drinking water is overwhelmingly a private-well issue, since surface water sources used by most municipal utilities are exposed to open air long enough for dissolved radon to off-gas naturally before treatment. If you are on a private well, especially in a region with granite, shale, or other uranium-bearing bedrock, testing is worth doing regardless of what your municipal neighbors experience.
Both, but inhalation is the bigger concern. The EPA's primary worry is radon gas releasing into household air during showers and other water use, which is linked to elevated lung cancer risk. Ingesting the water directly carries a smaller, secondary risk tied to stomach cancer, but treating the water addresses both exposure pathways at once.
A whole-house catalytic carbon system typically runs somewhere in the $900 to $1,300 range before installation, while a dedicated aeration system with a blower, vent, and repressurization pump typically starts around $1,400 and can run higher depending on well flow rate and installation complexity. Both are meaningfully more involved than a standard whole-house sediment or carbon filter, which is part of why confirming your actual level with a test before buying is worth the small upfront cost.