(CNN) - You might want to take a close look at that glass of water.
It appears many Americans, possibly up to 15 million, are drinking tainted water.
That's according to a study released by Northeastern University and the Environmental Working Group.
They say they found perfluorochemicals, or PFC's, in 162 drinking water systems across the U.S.
PFC's are often used in products like cookware and waterproof clothing.
Manufacturers have claimed the dangerous PFC’s are no longer used in these products.
The toxic chemicals are linked to health issues like cancer and weakened immune systems.
PFC's are not classified as a federally regulated water contaminant like lead or arsenic.
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