From history to policy to full-on drama, In Deep dives headfirst into the troubling state of the mysterious networks that keep our water clean and coming out of the tap. We explore when “out of sight, out of mind” could get us in deep doo-doo, because the ugly truth is that these complex systems are just as imperfect as the people who created them. In Deep will plumb the depths of the complex mysteries behind the clean water in our lives. It’s an engrossing tale that mirrors the very development of our present-day human civilizations — and is shockingly just as fallible.

Throughout human history, cities have grappled with how to keep excrement separate from drinking water. In the Middle Ages, gong farmers excavated human waste from city dwellers and took it to the countryside to be used as fertilizer. In the 19th century, cities grew so big, this wasn’t possible anymore. So excrement went into rivers like the Thames, which is where London, a city of 2 million people in 1850, got its drinking water. At the same time, cholera was killing tens of thousands of people. Nearly everyone thought cholera was transmitted through the air. But John Snow, a London physician, discovered dirty water was the cause.

Just how hard is it to keep wastewater out of our drinking water? Super hard. In this episode, we take a look at the lengths one great American city, Chicago, went to in order to keep the source of its drinking water clean. Reverse the flow of the river? Why not? Then we explore the origins of activated sludge — a century-old microbial goo that still cleans up our sewage today. We end with a scientist studying what a city’s wastewater can reveal about the severity of the COVID-19 pandemic.