Radon in one paragraph
Radon is a radioactive gas produced as uranium in rock naturally breaks down. You can't see, taste, or smell it, and breathing elevated levels over years is the second-leading cause of lung cancer in the U.S. Pennsylvania's geology — including the Reading Prong formation that runs through the Lehigh Valley and gave radon its national moment in the 1980s — makes this one of the most radon-prone states in the country. That's the air story. The water story is its quieter cousin.
How well water carries radon into your air
Groundwater moving through uranium-bearing rock dissolves radon the way soda holds carbonation. Open a tap — especially a hot, spraying one — and the gas escapes into the room. Showers, dishwashers, and laundry are the big releases. The working rule of thumb from Penn State and PA DEP: every 10,000 pCi/L of radon in water adds roughly 1 pCi/L to indoor air — against EPA's indoor-air action level of 4 pCi/L.
So water is rarely the main source. But Pennsylvania groundwater runs genuinely high: a USGS evaluation of three decades of PA samples found 87% at or above 300 pCi/L and 14% at or above 4,000 pCi/L, with the highest readings in exactly the crystalline-rock geology our region sits near. A well at 20,000–30,000 pCi/L — they exist here — is adding a meaningful slice to the household's total exposure.
The thresholds, honestly explained
There is no enforceable radon-in-water standard — for public systems or private wells. EPA proposed two numbers years ago and never finalized them: 300 pCi/L, or 4,000 pCi/L in states (like Pennsylvania) that run EPA-approved indoor-air radon programs. Those proposals are still the most useful yardsticks a homeowner has:
- Below ~2,000 pCi/L: the water's contribution to your air is tiny. Spend your attention on an indoor-air test instead.
- Mid thousands: gray zone — worth fixing if your air also tests elevated, since every source counts toward the same lungs.
- Above ~10,000 pCi/L: the water alone is adding 1+ pCi/L to your air; treatment is worth pricing on its own merits.
Air first — always
The order of operations matters, and it's the opposite of how water companies sometimes sell it. Most indoor radon seeps from the soil through the foundation; the fix for that is a sub-slab depressurization system installed by a radon mitigator — not water treatment. Test your air first (PA DEP recommends every home test, and kits are cheap). If air is elevated and you're on a private well, test the water to see how much of the problem arrives by pipe.
How water radon is removed
- Aeration (the gold standard). A whole-house unit bubbles air through incoming water and vents the stripped radon outside through a dedicated pipe — 95–99% removal at any concentration, minimal maintenance. EPA lists it as the best available technology; for high readings it's the only practical choice.
- Granular activated carbon (GAC). Works at lower concentrations and costs less up front — with one honest caveat: the carbon bed slowly accumulates radioactivity and must be replaced and disposed of properly every year or two, which erodes the savings at higher radon levels.
The honest bottom line
Radon in water is a genuinely Pennsylvanian problem, and also a genuinely secondary one: air first, water second. If you're on a well anywhere in our region — and especially if your basement has ever tested high — put the water test on your once-ever list alongside lead and arsenic. It costs less than dinner, and either answer is useful: a low number closes the question for good, and a high one has a proven, vented, one-and-done fix.