Every day, the Ohio River sends billions of gallons of water flowing past Louisville’s pumping station, where the Kentucky city’s utility sucks it up to turn it into tap water.
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 in the U.S., Louisville Water 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 cancer, reduced immune system functioning, high cholesterol, and developmental delays in children.
They’re also known as “forever chemicals” because their strong chemical structures make them degrade incredibly slowly in the environment.
Today, they litter soil and water sources around the world and can be found in the blood of almost everyone in the U.S.
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One type of PFAS that the Louisville water technicians are tracking is HFPO-DA, also known by a trade name, GenX.
Just over a year ago, workers noticed an unexpected increase in the level of GenX detected in a sample of the raw, untreated water drawn from the Ohio River for filtering and processing.
The GenX levels Louisville found in December 2024 were 15 times the reading from the previous month: 52 parts per trillion versus 3.4 ppt.
“A part per trillion is like one second in 32,800 years. Put your head around that, right?” said Peter Goodmann, the city utility’s director of water quality and research.
He offered another way to think of it: One part per trillion would be a single drop of water in 20 Olympic swimming pools.
Goodmann told KFF Health News and NPR he wasn’t worried about local customers’ safety, because the increased levels were still pretty low.
Risks posed by low PFAS concentrations are measured over a lifetime of exposure, he said. And recent data from Louisville shows the PFAS levels in city drinking water fell back within planned federal safety limit …