(CBS NEWS) -- More than half of Americans could be drinking tap water tainted with a radioactive element. A new report from the nonprofit Environmental Working Group (EWG) finds more than 170 million people are exposed to radium in their drinking water. That could increase the risk of cancer.

When Dennis Taylor moved with his wife and two kids back to her hometown of Brady, Texas, he quickly found out many there don't drink the city water, reports CBS News correspondent Anna Werner.

"I think I tried to drink out of the tap water and it was like, woah woah woah, no we don't drink out of the tap water," Taylor said.

But it was only recently that he learned that water has unacceptably high levels of a radioactive substance: radium, a contaminant that occurs naturally in the ground and winds up in aquifers. The city's radium levels violate the Environmental Protection Agency's (EPA) maximum allowable levels.

The reason it's of concern? Radium is a known carcinogen.

"It has been associated with increases in bone cancer. So exposure to radium… even low levels, may increase the risk of cancer development," said Alexis Temkin, toxicologist with the EWG.

EWG collected data from public water systems around the country and analyzed five years of tests from 2010 to 2015. Radium was found in all 50 states – and the group found 158 public water systems in 27 states "reported radium in amounts that exceeded the federal legal limit."

The state with the most widespread contamination, according to EWG, is Texas, where "more than 3,500 utilities serving more than 22 million people – about 80 percent of the state's population" reported finding radium.

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