When Cottage Grove, Minnesota's drinking-water panic began, Mayor Myron Bailey was at a conference. It was May 22, 2017, and the state health department wanted to give Bailey a heads-up. It was about to set a new, lower level for a type of unregulated chemical found in Minnesota's drinking water. And Cottage Grove's would exceed the new threshold. He had known for years that per- and polyfluoroalkyl substances (or PFAS) ... lingered in the water around Cottage Grove. 3M's factory had been churning out some varieties since the 1950s for the water- and stain-repellant Scotchgard. 3M also sold its PFAS to other companies to make Teflon, outdoor gear, greaseproof food papers and firefighting foams. Recent studies have linked widely used PFAS, including the varieties called PFOA and PFOS, to reduced immune response and cancer. That new evidence had stirred Minnesota's health department to act. There was always a perception in our community that cancer was caused by the drinking water," Bailey said, but after the state's announcement, "people freaked out." Water tests show that 110 million Americans have levels of PFAS in their water that the most cautious scientists call unsafe. At the same time, new studies show how the chemicals can cause harm even at tiny doses. As awareness spreads, 3M has been named in dozens of lawsuits, several this year alone. Some target industrial sources. But most focus on airports where the chemicals were sprayed onto the ground in firefighting foams.