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.