It’s raining. It’s not a storm: aboveground, people aren’t even opening umbrellas. But down below, there is trouble. Even a 20-minute shower will send millions of liters of extra liquid into the sewer system, overloading it. At that point, it does what it is allowed and designed to do and discharges sewage untreated into the nearest water body. This is legal, uncontroversial, and more common than you might think. Four percent of New York City’s shit goes straight into its harbor. In London, the Lesser Stink of 2004 poured 600,000 tons of sewage into the River Thames. Fish died in their hundreds; rowers rowed through used condoms and toilet paper. London’s water utility admitted discharging into the river once a week, in volumes enough to fill London’s Royal Albert Hall 525 times. In the sewerless world, meanwhile, 90 percent of sewage ends up in the sea, making it the biggest marine pollutant. Its pathogens can harm humans – hepatitis A can survive for 100 days in saltwater – but its nutrients are deadlier. The unwanted phosphorus and nitrogen that we ingest with food, then excrete in shit create perfect conditions for algae and other plant life to breathe. Too many can suck oxygen from the water, leaving none for any other aquatic life. The ecosystem suffocates, and another “dead zone” is formed. In 2003, there were 146 dead zones in the oceans; by 2008, there were 409.