Radon in Well Water: What New Jersey Homeowners Need to Know
Most New Jersey homeowners who think about radon think about the air in their basement. That’s the right instinct — soil gas is the dominant source of indoor radon exposure in the vast majority of homes. But for the roughly one million NJ residents on private wells, there’s a second radon pathway that gets far less attention: the water itself. Radon dissolves readily into groundwater as it moves through uranium-bearing bedrock, and every time that water is used inside the home — in the shower, at the sink, running the dishwasher — radon gas escapes into the indoor air. Understanding how waterborne radon works, how it connects to your air radon readings, and what treatment actually looks like is essential knowledge for any NJ homeowner on a private well.
How Does Radon Get Into Well Water?
Radon is a radioactive gas produced by the natural decay of uranium in rock and soil. It has no color, no odor, and no taste — the only way to know it’s present is to test for it. According to the U.S. Environmental Protection Agency, radon forms continuously wherever uranium-bearing geology exists, and it moves readily through fractured rock and soil into groundwater aquifers. When a private well draws water from those aquifers, the dissolved radon comes with it. Surface water sources — rivers, lakes, reservoirs — are not a meaningful concern because radon off-gasses quickly when water is exposed to open air. Private wells drawing from deep bedrock aquifers are the vulnerable pathway, which is why this is a well water issue and not a municipal water issue for most NJ homeowners.
The geology of northern New Jersey makes this particularly relevant for a large portion of the state’s private well users. The Highlands Province — covering significant portions of Sussex, Warren, Hunterdon, Morris, and Passaic counties, with parts of Bergen and Somerset — sits on bedrock formations with elevated natural uranium concentrations. As uranium decays, it produces radium, which in turn produces radon. Wells drilled into this bedrock draw water that has been in prolonged contact with these formations, and radon concentrations in those wells can be substantial. This is why the NJDEP expanded gross alpha testing requirements for private wells in northern NJ counties in 2018 — and why uranium testing is additionally required in certain counties based on local geology.
Why Is Radon in Water Different from Radon in Soil?
The mechanism is the same — uranium decay produces radon — but the delivery path into your home is different, and that changes both how you detect it and how you treat it. Soil gas radon seeps through foundation cracks, slab penetrations, and below-grade openings directly into the living space. Waterborne radon enters the home dissolved in the well water supply and is released into indoor air during normal water use. Showering is the most significant release point because hot water agitates and aerates the water, releasing dissolved gas efficiently into a small, typically enclosed space. Dishwashing, running faucets, and doing laundry all contribute as well, though at lower volumes. The radon released this way joins whatever radon is already present in the home’s air from soil gas, compounding the total indoor exposure.
What Is the Connection Between Radon in Water and Radon in Air?
This is the most important concept for NJ homeowners to understand, and it’s the reason waterborne radon matters even when air radon levels seem manageable. The EPA has established a widely used approximation: every 10,000 picocuries per liter (pCi/L) of radon in well water elevates the whole-house average indoor air radon concentration by approximately 1 pCi/L. This ratio is an average — actual transfer varies by home size, ventilation, and water use patterns — but it provides a practical framework for understanding how much your water is contributing to your air readings.
To put that in context: if your well water tests at 20,000 pCi/L of radon, it is likely contributing roughly 2 pCi/L to your indoor air level. The EPA’s action level for indoor air radon is 4 pCi/L — the point at which mitigation is recommended. If your air test comes back at 4.5 pCi/L and your water is contributing 2 of those picocuries, treating the water could bring your air level down to approximately 2.5 pCi/L without any changes to your foundation or ventilation. Conversely, if your air radon is elevated and you mitigate through sub-slab depressurization but don’t address radon in the water, you may find that air levels don’t drop as far as expected — because the water is still releasing radon into the living space every time it’s used.
How Much of My Indoor Radon Could Be Coming from the Water?
In most homes, water contributes a relatively small fraction of total indoor radon — the EPA estimates that only about 1 to 2 percent of indoor airborne radon nationwide comes from drinking water. But in northern NJ homes on private wells with high-uranium bedrock geology, that fraction can be meaningfully larger. The practical step is to test both: test the air first, since soil gas is almost always the dominant source, and then test the water if air levels are elevated or if the home draws from a bedrock well in one of the higher-risk northern counties. If you’ve already had air radon mitigated and levels remain stubbornly elevated, waterborne radon is worth investigating as a contributing source. Our radon mitigation service and our water radon treatment service address both pathways — and understanding which one is driving your readings matters before selecting an approach.
What Are the Health Risks of Radon in Well Water?
Radon in drinking water poses two distinct health concerns: inhalation of radon that off-gasses from water into indoor air, and ingestion of radon dissolved in the water itself. Of these two, inhalation is by far the more significant risk. The EPA estimates that approximately 89% of the cancer risk associated with waterborne radon comes from breathing the gas after it’s released from water — primarily in the form of lung cancer. The remaining 11% comes from ingestion, which has been associated with a small increased risk of stomach cancer at high chronic exposure levels. Radon in water is not detectable by taste, smell, or appearance, and the health effects of long-term exposure accumulate silently over years.
There is currently no federally enforced maximum contaminant level (MCL) for radon in drinking water. The EPA proposed but never finalized a federal standard, and private wells are not regulated by federal drinking water law in any case — private well owners are entirely responsible for their own testing and treatment decisions. New Jersey’s Drinking Water Quality Institute has recommended an MCL of 800 pCi/L for radon in public water systems, which provides a useful reference point. For private well owners, the practical guidance is to test, understand how your water radon level interacts with your air radon reading, and make a treatment decision based on the combined exposure picture rather than the water number in isolation.
- No color, odor, or taste — testing is the only way to detect radon in water
- Inhalation risk from off-gassing is roughly 8x greater than ingestion risk
- Showering releases radon most efficiently — small enclosed space, hot water, agitation
- No federal MCL for radon in private wells — testing and treatment are the homeowner’s responsibility
- NJ DWQI recommends 800 pCi/L as a reference threshold for public systems
- Elevated air radon that doesn’t fully resolve after mitigation may have a waterborne component
How Does Radon in Water Relate to NJ’s Overall Radon Risk Profile?
New Jersey is consistently ranked among the states with the highest radon risk in the country, driven primarily by its geology. The Reading Prong formation, which runs through northern NJ into Pennsylvania and New York, is one of the most radon-productive geological formations in the eastern United States. The NJDEP classifies municipalities by radon potential tier based on testing data — and many communities in Morris, Hunterdon, Somerset, Warren, and Sussex counties fall into Tier 1, meaning at least 25% of tested homes have exceeded the 4 pCi/L air action level. In these communities, private wells drawing from the same uranium-bearing bedrock that drives air radon are also at elevated risk for waterborne radon. The two problems share a geological root cause, which is why a comprehensive radon evaluation for any northern NJ home on a private well should include both air and water testing.
For home buyers, this is a particularly important due diligence item. A home inspection will not include radon testing unless it’s specifically requested and contracted. The PWTA requires gross alpha testing of private wells at the time of sale — and gross alpha includes radon as a component — but a gross alpha result alone doesn’t tell you how much of that radioactivity is radon specifically versus radium or uranium. Buyers purchasing homes in higher-risk northern NJ counties should request both an air radon test and a dedicated water radon test as part of their due diligence, separate from the PWTA minimum. Our guide on well water testing for NJ homeowners explains what a complete pre-purchase test should include and why the minimum legal requirement often isn’t enough.
| Radon in Water (pCi/L) | Estimated Air Contribution | Combined Risk Context | Recommended Action |
|---|---|---|---|
| Under 4,000 | Less than 0.4 pCi/L added to indoor air | Low contribution; air radon from soil is likely dominant | Address air radon first; retest water if air remains elevated |
| 4,000–10,000 | Roughly 0.4–1.0 pCi/L added to indoor air | Moderate; water is a meaningful contributor in high-air-radon homes | Consider water treatment alongside air mitigation |
| 10,000–20,000 | Roughly 1.0–2.0 pCi/L added to indoor air | Significant; water treatment likely needed to reach air targets | Point-of-entry aeration system recommended |
| 20,000–50,000 | Roughly 2.0–5.0 pCi/L added to indoor air | High; water alone may be pushing air above the 4 pCi/L action level | Point-of-entry aeration; also evaluate air radon sources |
| Above 50,000 | 5.0+ pCi/L added to indoor air | Severe; water is a primary driver of indoor radon exposure | Immediate point-of-entry treatment; professional system design required |
How Is Radon Removed from Well Water?
Two treatment technologies are used for waterborne radon, and they are not interchangeable. Point-of-entry aeration systems are the most effective approach — they work by exposing the water to air before it enters the home’s distribution system, allowing dissolved radon gas to escape harmlessly to the outdoors rather than releasing inside. Properly installed aeration systems can remove 95% or more of waterborne radon and are the preferred method for any home with radon concentrations above roughly 10,000 pCi/L. Because the radon is vented externally, there is no radioactive accumulation in the treatment equipment itself, which makes long-term maintenance straightforward.
Granular activated carbon (GAC) filters are the alternative and work by adsorbing radon onto the carbon media as water passes through. They are effective at lower radon concentrations — generally below 10,000 pCi/L — but carry an important limitation: the radon and its decay products accumulate in the carbon over time, eventually making the filter media radioactive. This has implications for maintenance scheduling, handling of spent cartridges, and disposal, which must be managed by a licensed professional. For homes with higher radon concentrations in the water, GAC is generally not the recommended path. Jersey Radon’s team installs and services both system types, and our approach always begins with water testing to determine which technology is appropriate for your specific conditions. Our radon removal service page and water radon treatment page cover the options in more detail.
Does Treating Water Radon Eliminate the Need for Air Radon Mitigation?
Not necessarily, and this is a distinction that matters. Because soil gas is the dominant source of indoor radon in most homes, treating the water will reduce air radon levels by the amount the water was contributing — but if soil gas is also elevated, treating the water alone will not bring air levels to an acceptable range. The two sources must be evaluated and addressed independently. In a home where air radon is 6 pCi/L and 2 pCi/L of that is coming from water, treating the water brings the air level to approximately 4 pCi/L — right at the action level threshold but not below it. Both air mitigation and water treatment would be needed to reach levels the EPA considers optimal. This is why testing both before committing to a treatment strategy is the only approach that produces a reliable result, and why Jersey Radon’s licensed team evaluates the full picture before recommending any system.
What Should NJ Home Buyers Know About Radon in Well Water?
Radon in well water is one of the most consistently underdetected issues in NJ real estate transactions involving private wells. The gross alpha test required by the PWTA catches radioactivity broadly but doesn’t isolate radon specifically — and a result that appears to pass the gross alpha threshold can still carry waterborne radon at levels worth treating. An air radon test, which is not required by the PWTA, may be requested by a buyer’s lender or attorney but is often left to the buyer to arrange independently. In high-radon counties in northern NJ, entering a real estate transaction without independent air and water radon testing is taking on a risk that is entirely avoidable with two straightforward tests.
If you are buying a home in New Jersey with a private well — particularly in Hunterdon, Morris, Warren, Sussex, Somerset, or Passaic counties — we strongly recommend adding both air and water radon testing to your pre-purchase inspection list. If you currently own a home on a well and haven’t tested either in the past two years, the same applies. Contact our team for a free estimate or call us at (732) 357-1988. We are licensed and insured to evaluate and treat both air radon and waterborne radon throughout New Jersey, and we serve residential homeowners and buyers across the entire state.
