If it’s not stuck in glaciers or polar ice, 99 per cent of the world’s freshwater is groundwater. Water underground supplies nearly half of the world’s drinking water. But what happens when dangerous chemicals and waste – polyfluoroalkyl substances (PFAS), oil, gasoline and road salts – percolate down into that supply?    On this episode of What About Water? Jay sits down with the father of contaminant hydrogeology, Dr. John Cherry, to talk about the water under our feet, and how we can better monitor it. In the 1970s, Cherry wrote the foundational textbook on groundwater with his colleague, Al Freeze. And we hear how one of his students paved the path for his successful career in the field. To find out what’s actually being done to stop industry polluters from dispersing PFAS chemicals into our waterways, producer Erin Stephens speaks with Marc Yaggi, CEO of the global nonprofit Waterkeeper Alliance. Yaggi shares what Waterkeeper is advocating for in Congress, brands eliminating PFAS from their production lines, and how everyone can get involved in the effort to get these “forever chemicals” out of our rivers. Check out their surface water quality survey here to learn more. Got a question for Jay? Write to us at ideas@whataboutwater.org and you may hear your question in an upcoming episode. Voice memos are also welcome!