Wednesday the Environmental Protection Agency announced new drinking water standards to limit people's exposure to some PFAS chemicals. For decades, PFAS have been used to waterproof and stain-proof a variety of consumer products. These "forever chemicals" in a host of products — everything from raincoats and the Teflon of nonstick pans to makeup to furniture and firefighting foam. Because PFAS take a very long time to break down, they can accumulate in humans and the environment. Now, a growing body of research is linking them to human health problems like serious illness, some cancers, lower fertility and liver damage. Science correspondent Pien Huang joins the show today to talk through this new EPA rule — what the threshold for safe levels of PFAS in tap water is, why the rule is happening now and how the federal standards will be implemented.

Read more of Pien's reporting on the EPA's first ever rule on PFAS in drinking water.

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A study by the U.S. Geological Survey found that the man-made chemicals are present in nearly half the country's tap water supply.

A new government study estimates that at least 45% of the nation's tap water could be contaminated with one or more forms of PFAS. Here's what to do if you're worried about what's in your faucet.