Radon in Drinking Water
Found in 283 water systems • radioactive
Updated September 2026 • Data from EWG & EPA
What is Radon and Why Does It Matter?
RADON IN YOUR TAP WATER: WHAT YOU NEED TO KNOW
What Radon Is and How It Gets Into Your Water
Radon is a colorless, odorless radioactive gas that comes from the natural decay of uranium in soil and rock. When groundwater passes through radon-rich geological layers, it dissolves into the water. Unlike surface water sources, groundwater systems are particularly vulnerable—radon can accumulate in wells and underground aquifers over time. Once radon enters your home's water supply, it can be released into the air when you shower, wash dishes, or run your tap. This means radon exposure happens two ways: drinking contaminated water and breathing radon gas that escapes during water use. Studies suggest that inhalation accounts for about 80% of radon exposure from tap water, while ingestion accounts for the remaining 20%.
The Health Risks of Radon Exposure
Radon is a known carcinogen. The EPA and WHO classify it as a cause of lung cancer, particularly with long-term exposure. Radon damages the cells lining your lungs and airways, increasing cancer risk over years of exposure. The risk is dose-dependent—higher radon levels mean greater danger. The EPA estimates that radon is responsible for about 21,000 lung cancer deaths annually in the United States, making it the second leading cause of lung cancer after smoking. Children may face particular concern since they have more years of potential exposure ahead. Most people exposed to radon show no immediate symptoms, which makes it especially insidious—you won't know there's a problem without testing.
Regulatory Standards and the EWG Guideline Gap
The EPA set a Maximum Contaminant Level (MCL) for radon at 4,000 pCi/L (picocuries per liter) in 1991. However, the Environmental Working Group (EWG), which bases its guidelines on additional health research, recommends a much stricter level of 0.15 pCi/L. This massive gap exists because the EWG factors in lifetime cancer risk and uses more conservative safety assumptions than the EPA. Our data reveals the scope of the problem: 280 out of 283 water systems tested exceeded the EWG guideline, with an average radon level of 1,264 pCi/L. The maximum recorded level reached 31,100 pCi/L—over 200 times the EWG recommendation. This discrepancy means that water meeting EPA standards may still pose significant health risks according to independent health research.
Geographic Hotspots: Where Radon Risk Is Highest
Radon contamination follows geological patterns. Maine leads with 69 affected systems, followed by Wisconsin (40), California (39), Nevada (34), and Massachusetts (18). These states share common geology: granite bedrock, glacial deposits, and other uranium-bearing formations that generate radon. Maine and Massachusetts sit atop ancient granites in New England. Wisconsin's glacial geology creates conditions favorable for radon accumulation. Nevada's mining-rich geology and California's diverse terrain both contain significant radon sources. If you live in these regions—or in any area with granite bedrock, shale, or phosphate deposits—your groundwater risk is elevated. Even within these states, risk varies by neighborhood based on local geology.
Removing Radon From Your Tap Water
Radon requires specific treatment because standard carbon filters don't remove it effectively. Aeration systems work by bubbling air through water, which releases radon gas before you drink it. Granular activated carbon (GAC) filters can remove some radon, though they're more effective for other contaminants. Reverse osmosis systems provide excellent radon removal, typically eliminating 90-99% of dissolved radon. For comprehensive protection, combining aeration with other filtration methods works best. If radon is your primary concern, an aeration system paired with a quality multi-stage filter offers cost-effective results. The first step is testing your water—you can't address a problem you don't know exists. Once you know your radon level, you can choose the right filtration approach for your home's specific situation.
Regulatory Standards for Radon
| Standard | Level | Notes |
|---|---|---|
| EWG Health Guideline | 1.50 pCi/L | Stricter, based on latest science |
| Average Detected Level | 1,264.45 pCi/L | Across all tested systems |
| Highest Detected Level | 31,100 pCi/L | Worst-case system |
Cities With the Highest Radon Levels
| # | City | Detected Level | People Served |
|---|---|---|---|
| 1 | Bridgton, ME | 31,100 pCi/L | 152 |
| 2 | Leicester, MA | 23,539.25 pCi/L | 140 |
| 3 | Oxford, MA | 18,201.67 pCi/L | 50 |
| 4 | Charlton, MA | 15,633.33 pCi/L | 26 |
| 5 | Oxford, MA | 14,696.67 pCi/L | 40 |
| 6 | Moultonborough, NH | 14,000 pCi/L | 208 |
| 7 | East Kingston, NH | 12,200 pCi/L | 72 |
| 8 | Standish, ME | 8,695.14 pCi/L | 40 |
| 9 | Portland, ME | 7,056.09 pCi/L | 30 |
| 10 | Hollis, ME | 5,513 pCi/L | 32 |
| 11 | Waldoboro, ME | 5,272.50 pCi/L | 70 |
| 12 | Franklin, ME | 5,021.57 pCi/L | 45 |
| 13 | Pike, NH | 4,208 pCi/L | 76 |
| 14 | Upton, MA | 3,969.50 pCi/L | 80 |
| 15 | Tyngsborough, MA | 3,965 pCi/L | 60 |
States Most Affected by Radon
How to Remove Radon From Your Water
Standard pitcher and refrigerator filters cannot remove radon gas; radon requires either whole-house aeration systems with proper venting to remove dissolved radon, or GAC systems sized and maintained specifically for radon reduction, which must be professionally installed and regularly monitored.
Standard pitcher filters and carbon-only filters do not reliably remove Radon. A reverse osmosis system with NSF/ANSI 58 certification is the most reliable solution.
Effective radon removal requires either soil depressurization (venting radon from beneath the home), whole-house aeration systems, or large granular activated carbon units professionally sized and maintained with regular testing to confirm effectiveness.
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Shop Hydrogen FlaskFrequently Asked Questions
Is Radon in my drinking water?
Radon was detected in 283 water systems across the US. Check your city's water quality report to see if it affects your water supply.
What are the health effects of Radon in water?
Radon has been associated with various health concerns at elevated levels. The EWG has set health guidelines that are typically stricter than EPA legal limits.
Which city has the most Radon in its water?
Based on our analysis, Bridgton, ME has the highest detected levels of Radon in its water supply.
How do I remove Radon from my water?
Reverse osmosis (RO) systems are generally the most effective at removing this contaminant. Check the filtration recommendations section for specific guidance.
Related Contaminant Guides
Data sources: Environmental Working Group (EWG) Tap Water Database, U.S. EPA Safe Drinking Water Information System (SDWIS)
Last updated: September 2026
Methodology: Contaminant levels are compared against both EPA legal limits (Maximum Contaminant Levels) and EWG health guidelines, which are often stricter and based on the latest scientific research.
