Radon and Well Water in Central New York

Most radon discussion focuses on soil gas seeping into basements. But radon also dissolves in groundwater, and if your home draws from a private well, that water can carry radon indoors — where it gets released into the air every time someone showers, runs the dishwasher, or does laundry.

This matters in the rural parts of Onondaga County, where private wells are common. It is a real issue, though it is worth getting the proportions right rather than overstating it.

How Radon Gets Into Well Water

The same uranium decay that produces soil gas also produces radon underground, where groundwater is moving through rock and sediment. Radon dissolves readily in water, so groundwater in contact with uranium-bearing rock picks it up.

Drilled bedrock wells tend to carry more radon than shallow dug wells, because they draw from deeper rock formations where water has had extended contact with mineral surfaces and where dissolved gas cannot readily escape.

Municipal water is generally not a concern. Public systems typically draw from surface sources or treat and store water in ways that allow dissolved radon to escape long before it reaches a tap. If you are on Onondaga County Water Authority or a similar municipal supply, waterborne radon is not something you need to investigate.

This is fundamentally a private well question.

Two Different Exposure Routes

Radon in water creates risk two ways, and one dominates.

Inhalation. When water is agitated or heated — showering, dishwashing, laundry — dissolved radon comes out of solution into indoor air. You then breathe it. This is the primary concern.

Ingestion. Drinking water containing radon carries some risk to the stomach lining. Research indicates this is a much smaller contribution than inhalation.

The practical implication is slightly counterintuitive: the risk from radon in water is mostly about air quality, not drinking water safety. Which also means that a bathroom exhaust fan running during showers does meaningful work.

The Rough Conversion

A widely used approximation holds that roughly 10,000 pCi/L of radon in water contributes about 1 pCi/L to indoor air.

That ratio is worth sitting with, because it puts the issue in perspective. Water would need to contain very high radon concentrations to be the main driver of an elevated indoor air reading. A well at 5,000 pCi/L contributes roughly 0.5 pCi/L to the air — real, but not enough on its own to push a home over the 4.0 action level.

Conversely, a well at 40,000 pCi/L would contribute roughly 4 pCi/L, which is entirely capable of putting a home over the threshold by itself.

The ratio is an approximation. Actual contribution depends on household water use, home volume, and ventilation. A large family showering daily in a tight home moves more radon from water to air than a single occupant in a leaky farmhouse.

Testing Order Matters

Because soil gas is the dominant source in the overwhelming majority of homes, the sensible sequence is air first.

Start with an air test. Standard indoor radon testing in the lowest livable level tells you whether you have an elevated reading at all. If air is below the action level, waterborne radon is not creating a problem you need to solve.

If air is elevated, address soil gas first. In most homes with a private well, soil gas is still the main contributor. A sub-slab depressurization system is the standard fix.

Test the water if air stays elevated after mitigation. This is the situation that points toward water as a meaningful source — a properly installed soil gas system that should have brought levels down, but did not fully. If a well is contributing several pCi/L to the air, no amount of sub-slab suction will remove it.

Water testing is also reasonable earlier if you are already testing well water for other contaminants, if you are buying a rural property with a drilled bedrock well, or simply if you want a complete picture.

How Water Testing Works

Radon in water requires a specific collection method, because the whole point is measuring a dissolved gas that wants to escape.

Samples are collected in special vials filled to eliminate any air gap, taken from a tap as close to the well as possible and before any treatment equipment. The sample must not be aerated during collection — you cannot let it splash — and it needs to reach the lab quickly, since radon has a short half-life and the measurement is time-corrected.

This is not a general water quality test. A standard well panel checking bacteria, nitrates, and hardness will not include radon unless you specifically request it. Ask for radon in water testing by name.

Treatment Options

If water testing shows radon high enough to matter, there are two established treatment approaches, both installed at the point where water enters the home.

Aeration is generally considered the preferred method for higher concentrations. Water is sprayed or bubbled in a tank, allowing dissolved radon to come out of solution, and the released gas is vented outdoors. Aeration systems handle high concentrations effectively and do not accumulate radioactivity.

Granular activated carbon filtration passes water through a carbon bed that adsorbs radon. GAC units are typically less expensive than aeration and work well at lower to moderate concentrations. The tradeoff is that the carbon accumulates radioactivity over time, which creates handling and disposal considerations and means placement away from occupied space matters.

Both are point-of-entry systems treating all water entering the home. A point-of-use filter at the kitchen sink does essentially nothing for radon, because the dominant exposure route is inhalation from showers and appliances elsewhere in the house.

Who Should Look Into This

You have reason to consider water testing if you are on a private well — particularly a drilled bedrock well — and any of the following apply: your indoor air tested elevated, your air stayed elevated after a properly installed mitigation system, you are purchasing a rural property with a well, or you simply want the complete picture.

If you are on municipal water, you can set this aside entirely and focus on soil gas.

Onondaga County’s Zone 1 designation reflects soil and bedrock conditions that produce radon — the same conditions that put it into groundwater. For most homes here, soil gas is the story and water is a footnote. But in the rural stretches of the county, on a deep bedrock well, the footnote occasionally turns out to matter.

Questions about radon in your home or well? Call (315) 234-2853. We serve Syracuse, Cicero, Liverpool, Baldwinsville, Camillus, Manlius, DeWitt, and surrounding Onondaga County communities.

Private wells are most common on the outskirts of the county, including parts of Manlius near the limestone quarries and rural stretches of Cicero north toward Oneida Lake.