OLR Research Report

October 18, 2006




By: John Kasprak, Senior Attorney

You asked if Connecticut regulates radon in drinking water. You are interested in any standards set by neighboring states and any processes for addressing unacceptable levels of radon in water.


Connecticut, as well as its neighboring states, has not adopted formal regulations on radon in drinking water, but has guidelines and recommendations for homeowners.

The federal Safe Drinking Water Act requires the Environmental Protection Agency to adopt a regulation setting a drinking water standard for radon. While a regulation has been proposed and been the subject of discussion, there is currently no federally enforced drinking water standard for radon.


Radon is a gas that has no color, odor, or taste. It comes from the natural radioactive breakdown of uranium in the ground. You can be exposed to radon by two main sources: (1) in the air in your home and (2) in drinking water. Radon is also found in small amounts in outdoor air. Most of the radon in indoor air comes from soil underneath the home. As uranium breaks down, radon gas forms and seeps into the house. Radon from soil can get into any type of building and build up to high levels in the air inside the structure.

Radon gas can also dissolve and accumulate in water from underground sources (groundwater), such as wells. When water that contains radon is used in the home for showering, washing dishes, and cooking, radon gas escapes from the water into the air. (This is similar to carbonated soda drinks where carbon dioxide is dissolved in the soda and is released when you open the bottle.) Some radon stays in the water. Radon generally is not a concern in water that comes from lakes, rivers, and reservoirs (surface water), because the radon is released into the air before it reaches the tap.

The federal Environmental Protection Agency (EPA) estimates that only about 1 to 2% of radon in the air comes from drinking water. But breathing radon released into the air from tap water increases the risk of lung cancer over a lifetime. Drinking water containing radon presents a risk of developing internal organ cancers, such as stomach cancer. But the EPA notes that this risk is smaller than the risk of developing lung cancer from radon released into the air from tap water.


The federal Safe Drinking Water Act (SDWA) mandates that EPA issue a regulation setting a drinking water standard for radon. But to date it has not and there is no federally-enforced drinking water standard for radon. In setting such a standard, the law requires EPA to, among other things, consider the costs and benefits of control programs for radon from other sources, such as air. While EPA does not directly regulate radon in indoor air, the SDWA authorizes EPA to set a drinking water standard that allows states and water systems to offset high radon levels in drinking water with reductions of radon levels in indoor air (see “Drinking Water-Revisions to EPA's Cost Analysis for the Radon Rule Would Improve its Credibility and Usefulness,” U.S. General Accounting Office (GA0), Report No. 02-333, February 2002).

In a proposed rule issued in 1999, EPA presented a complex drinking water regulation that used the framework for regulating radon specified in the SDWA. The regulation would apply to community water suppliers (water systems serving 25 or more year-round residents.) EPA does not regulate private wells.

Under the proposed regulation, states and water systems could, for the first time, choose one of two different standards, or limits, for a drinking water contaminant. The first standard reflects the typical regulatory approach under the SDWA imposing a health-based limit on the level of radon in drinking water and requiring water systems to provide drinking water that does not exceed the limit. The second or “alternative standard,” would allow considerably higher levels of radon in drinking water. But the standard may only be used when an EPA-approved program to reduce radon in indoor air is also implemented. The alternative method allows higher levels of radon in drinking water because the associated health risks are offset by reduced exposure to radon in indoor air.

The alternative standard (known as the “alternative maximum contaminant level”) would require community water suppliers to provide water with radon levels no higher than 4,000 pCi/L (picoCuries per liter, a unit of measurement for radiation), which contributes about 0.4pCi/L of radon to indoor air. Again, this requirement assumes that the state is also taking action to reduce radon levels in indoor air by developing EPA-approved, enhanced state radon in indoor air programs (called Multimedia Mitigation Programs).

For states that choose not to develop enhanced indoor air programs, the EPA proposed rule would require community water suppliers to reduce radon levels in drinking water to 300 pCi/L. This amount contributes about 0.03 pCi/L of radon to air in a home. Even if a state does not develop an enhanced indoor air program, it can choose to develop its own local indoor radon program and meet the standard of 4,000 pCi/L for drinking water.

EPA's proposed rule can be found at

EPA has set an advisory “action level” of 4 pCi/L for radon gas in indoor air. While not a mandated health standard, this level is a guideline for use in assessing the seriousness of exposure to airborne radiation.



According to the Connecticut Department of Public Health (DPH), “in the absence of a radon maximum contaminant level, DPH recognized the need to establish a guideline that homeowners could use to make an informed decision about whether to treat their private well water supply.” DPH recommends to homeowners served by a private well to consider treatment if their average annual (two or more samples in one year) radon in water is 5,000 pCi/L or greater. DPH states that once EPA promulgates a regulatory standard for radon in water, it “will explore the

feasibility of adopting the standards for the Connecticut private well water regulations.” (see for more information on Connecticut's radon program.

A 1990 Public Act (PA 90-114; CGS 19a-37b) required DPH to adopt regulations establishing acceptable levels of radon in ambient air and drinking water in schools by January 1, 1991. These regulations were never promulgated.

Rhode Island

The Rhode Island Department of Health recommends that if indoor air levels of radon are 4 pCi/L or higher, the home's well water be tested at a state certified laboratory. The department notes that if the well water contains elevated levels of radon, the levels that may be considered safe or unsafe depends on the levels detected in indoor air and whether the homeowner takes steps to reduce indoor air levels. The design of a treatment system for radon in air should consider radon levels in water where applicable. If an individual is served by a public drinking water system, he should call his supplier and find out is the water comes from a surface or ground water source.

If there are elevated levels of radon in the water or air, Rhode Island law requires that the person contract with a licensed radon mitigation contractor to install treatment systems for water and air.

New Hampshire, Maine, Massachusetts, Vermont

New Hampshire has no water quality standards for private wells in the state. The state cites the proposed EPA standards in its literature, stating that it believes that it is unlikely that the future EPA radon standard would exceed 4,000 pCi/L (see

Maine recommends a standard for radon in water of 4,000 pCi/L; Massachusetts 10,000 pCi/l, and Vermont 5,000 pCi/L.