What is Radon* and Why Does It Matter?

Radon in Tap Water: What You Need to Know

Radon is a naturally occurring radioactive gas. It forms underground when uranium and radium — elements found in soil and rock — break down over time. Most people associate radon with basements and indoor air, but it also dissolves into groundwater as it moves through rock formations. When that groundwater feeds a private well or a public water system, radon comes along with it. Homes that use well water are at higher risk, but municipal systems drawing from underground aquifers can carry radon too.

The health concern with radon is serious, though it's important to keep it in perspective. Radon in water poses two types of risk. First, when you drink radon-contaminated water, it can increase the risk of stomach cancer over time. Second — and more significant — radon releases into the air when water is used for showering, cooking, or washing dishes. Breathing that air is the bigger danger. The EPA estimates that radon in drinking water causes about 168 deaths per year in the United States, with lung cancer accounting for 89% of those deaths (EPA). At the levels found in this data — with an average of 423.95 pCi/L and a peak of 2,782.48 pCi/L — the risk is real and worth addressing.

The EPA has proposed a Maximum Contaminant Level (MCL) of 300 pCi/L for radon in public drinking water, but that rule has never been finalized. The EWG sets its health guideline lower, at 0.1 pCi/L — a level that reflects what researchers consider a negligible lifetime cancer risk. Every single one of the 50 water systems in this dataset exceeds that EWG guideline. The gap between the proposed EPA limit and the EWG guideline is wide, and the average level of 423.95 pCi/L sits above even the EPA's unfinalized standard. That means many Americans are drinking water with radon levels that no federal rule currently requires utilities to fix.

Geography plays a major role in radon exposure. California leads this dataset with 26 affected systems, followed by Missouri with 10, Wisconsin with 4, New Jersey with 3, and Kansas with 2. This pattern reflects geology more than anything else. States with granite-rich bedrock — like parts of California and New Jersey — tend to have higher uranium concentrations in the ground, which means more radon in the water. Missouri and Wisconsin sit on older rock formations that also release radon readily. If your home draws water from a well or from a utility that uses groundwater, and you live in one of these states, testing your water is a smart first step.

The good news is that radon in water is treatable. Two methods work well. Aeration treatment — which exposes water to air and lets radon escape as a gas — removes up to 99% of radon from water. Activated carbon filters are the other option, and they work effectively at the point of use, meaning right at your tap. A quality under-sink or whole-home filtration system with activated carbon can significantly reduce radon levels in your drinking water. Echo Water's systems use activated carbon filtration designed to target exactly these kinds of dissolved contaminants. If you're concerned about radon in your water, start by getting your water tested — a certified lab can give you a precise number to work with. From there, you can choose the right filtration approach for your home and your family's needs.

Regulatory Standards for Radon*

Cities With the Highest Radon* Levels

States Most Affected by Radon*

Frequently Asked Questions

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