Last updated 2026-07-17
About 1.1 million New Jerseyans — roughly 12 percent of the state — get their water from private wells. In the uranium-bearing geology of northern and western NJ, that water can carry dissolved radon into the house, where it off-gasses every time someone showers or runs the dishwasher. Here’s what the rules actually require, how to test, and what treatment costs.
New Jersey’s Private Well Testing Act (in effect since September 14, 2002) requires the untreated well water to be tested when a property with a private well is sold, and requires landlords to test every five years. The statewide parameter list covers coliform bacteria, nitrate, pH, iron, manganese, lead, arsenic, gross alpha particle activity, volatile organics, synthetic organics, and PFOA/PFOS/PFNA. Two county add-ons apply: mercury in nine southern counties, and uranium in twelve northern counties (Bergen, Essex, Hudson, Hunterdon, Mercer, Middlesex, Morris, Passaic, Somerset, Sussex, Union, Warren).
Radon in water is not a required PWTA parameter anywhere in New Jersey. The closest the law gets is gross alpha — a general radioactivity screen, required statewide since 2018 (twelve counties since 2008). NJDEP’s guidance: if gross alpha exceeds 15 pCi/L, follow-up testing for uranium, radium-226/228, and radon is recommended; between 5 and 15 pCi/L, radium testing is recommended. So a PWTA report can point toward a radon-in-water problem, but it will never state one directly. If you’re buying a well-water home in a Tier 1 municipality (see the NJ tier map explained), ordering the radon-in-water test yourself is the only way to know.
| Standard | Level | Status |
|---|---|---|
| Federal MCL | — | None exists; 1999 proposal never finalized |
| EPA 1999 proposed MCL | 300 pCi/L | Proposed only |
| EPA 1999 proposed AMCL (states with indoor-air programs) | 4,000 pCi/L | Proposed only |
| NJ Drinking Water Quality Institute recommendation | 800 pCi/L | Public water systems only; not adopted for private wells |
| Common industry action point (AARST guidance) | ~4,000 pCi/L | Rule of thumb, not law |
Private well owners are on their own here — no agency will make you test or treat. The practical convention in the industry is to consider treatment somewhere around 4,000 pCi/L, and to strongly consider aeration at 10,000+ pCi/L.
EPA’s working relationship is that 10,000 pCi/L of radon in water contributes about 1 pCi/L of radon to indoor air — its proposed 4,000 pCi/L standard corresponds to about 0.4 pCi/L added indoors, and 300 pCi/L to about 0.03 pCi/L. Waterborne radon also carries a small direct ingestion risk: of the roughly 168 annual U.S. cancer deaths EPA attributes to radon in drinking water, 89 percent are lung cancers from breathing radon released out of the water and 11 percent are stomach cancers from drinking it.
Keep the scale in perspective: EPA estimates only 1–2 percent of indoor-air radon comes from water in most homes. If your basement tests at 8 pCi/L, the fix is almost always a sub-slab mitigation system, not a water system. Water treatment is for the well-water homes where a water test confirms thousands of pCi/L.
A radon-in-water test is a lab analysis of a carefully collected sample (no aeration during collection). Mail-in kits run about $80–$170 including lab fees; NJ-certified labs and radon measurement businesses also collect samples during well inspections. Sequence it sensibly: run a cheap air test first, and add the water test if air is elevated and you’re on a well.
| Aeration (point of entry) | Granular activated carbon (GAC) | |
|---|---|---|
| How it works | Bubbles air through water in a tank; vents radon gas outdoors above the roofline | Adsorbs radon onto a carbon bed as water passes through |
| Removal | ~98–99% | Often quoted 50–80%+ at modest levels |
| Best for | Higher levels (industry guidance: above ~4,000–5,000 pCi/L, and effectively required at very high levels) | Lower levels, generally under ~4,000 pCi/L |
| Installed cost | ~$4,000–$7,000 (complex installs higher) | ~$1,200–$3,000 |
| Ongoing | Annual service, blower maintenance; may need repressurization pump | Media replacement every 1–2 years; spent carbon accumulates radioactivity and can require special disposal |
Aeration is the gold standard: it removes up to 99 percent of waterborne radon and doesn’t concentrate radioactivity anywhere in your house. GAC’s low upfront price is attractive, but the carbon bed becomes a low-level radiation source as it loads up — which is why professionals steer away from GAC at higher concentrations. Whoever installs, retest both water and indoor air afterward to confirm the numbers actually dropped.
The PWTA won’t test your well for radon — at most, a high gross alpha result will hint at it. In Tier 1 country on a private well, spend the ~$100–$170 on a water test when your air test comes back elevated, and price aeration if the water is carrying a four-figure radon load.
No. The PWTA requires testing at sale or lease for coliform bacteria, nitrate, pH, iron, manganese, lead, arsenic, gross alpha, VOCs, synthetic organics, and PFOA/PFOS/PFNA — plus mercury in nine southern counties and uranium in twelve northern counties. Radon in water is not on the list anywhere in the state. NJDEP does recommend radon testing as a follow-up when a well's gross alpha result exceeds 15 pCi/L.
No enforceable limit applies to private wells. There is no federal MCL — EPA proposed 300 pCi/L (with a 4,000 pCi/L alternative) in 1999 but never finalized the rule — and New Jersey's Drinking Water Quality Institute recommended an 800 pCi/L MCL for public water systems, which doesn't bind private wells. Practically, most professionals treat around 4,000 pCi/L as a reasonable action point.
The standard rule of thumb, used by EPA, is that every 10,000 pCi/L of radon in water contributes roughly 1 pCi/L of radon to indoor air as the water off-gasses during showers, laundry, and dishwashing. In most homes only 1–2 percent of airborne radon comes from water — the soil under the foundation is almost always the bigger source.
Point-of-entry aeration — the fix for higher concentrations — typically runs about $4,000–$7,000 installed, with some complex installs quoted higher. Granular activated carbon (GAC) runs roughly $1,200–$3,000 installed but is generally only appropriate below about 4,000 pCi/L, and the media accumulates radioactivity and needs periodic replacement.
Air first. It's cheaper (free to ~$50 DIY), and it measures the thing that actually causes most of the risk. If your air result is elevated and you're on a private well — especially in the Tier 1 geology of northwestern NJ — add a radon-in-water test (about $80–$170 by mail-in lab kit) to see how much the water is contributing.
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