The Ohio River sends billions of gallons of water flowing past Louisville, Kentucky's pumping station every day, where the city's utility sucks it up to turn it into tap water.

This story was produced in partnership with KFF Health News .

To ensure it tastes good and is safe to drink, a small team of scientists and technicians is constantly testing the water for pH, odors, heavy metals and microbes.

But unlike many smaller municipal utilities across the U.S., the Louisville Water Company regularly checks for PFAS ( per- and polyfluoroalkyl substances ).

That's a class of chemicals, used by manufacturers for decades to make things like nonstick pans, cosmetics, raincoats, food wrappers and firefighting foam.

Research studies have linked PFAS to health risks like cance

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