Arsenic, uranium, and radon in well water

USGS says these come mainly from natural sources in rock. A well can have them with no pollution nearby, and only a test tells you.

What USGS found in private wells

"In a study of 2,100 domestic wells, water pumped from about one in five wells contained one or more contaminants at a concentration greater than a human-health benchmark for drinking water." (USGS)
The most common were metals, radionuclides, and nitrate, "all of these but nitrate are derived primarily from natural sources." (USGS)

"Arsenic occurs naturally as a trace component in many rocks and sediments." (USGS)
USGS: "dangerously high levels of arsenic have been found in drinking water wells in more than 25 states in the United States." (USGS)
"Detections were more common and concentrations generally were higher in the west than in the east." (USGS) USGS also maps high-arsenic well use by county.
EPA's limit is 10 parts per billion (0.010 mg/L). (EPA) Check a result

"Radionuclides occur naturally in many rocks and minerals." "The most common examples of radionuclides in groundwater are uranium, radium, and radon." (USGS)
EPA's limits: uranium 30 micrograms per liter, radium 226 and 228 combined 5 pCi/L. (EPA) Check a result

There is no federal limit for radon in drinking water. Why
EPA: "Most of your risk from radon in water comes from radon released into the air when water is used for showering" and other household uses. (EPA Citizen's Guide to Radon)
"Compared to radon entering the home through water, radon entering your home through the soil is usually a much larger risk." (EPA) So test the air first: find a radon test kit.
"If you've tested the air in your home and found a radon problem, and your water comes from a well, have your water tested." (EPA)

Of the public programs we list, 78 test for arsenic, 13 for uranium, radium, or radioactivity, and 7 for radon. Find one near you
By mail: Tap Score Essential Well, $209, includes arsenic (Tap Score). Radon in water, $145 (Tap Score). Prices checked October 2, 2026.

We earn a small commission on Tap Score sales, which helps more people find low-cost water testing.

USGS and EPA pages checked October 2, 2026.