Deep beneath the city, an intricate network of pipes and pumps carries our waste to treatment facilities. Ideally, the entire process is hidden from the eyes — and nose — of the urban dweller who, from the moment the toilet flushes, remains blissfully unaware of what it takes to direct billions of gallons of wastewater out of a city.

The development of sewer infrastructure is one of the perks of modern urban living, rendering the consequences of our daily habits out of sight, out of mind — until it doesn’t.

In the US and beyond, many sanitation systems date back to the early 20th century or earlier, and they’re showing their age: Increasingly heavy downpours as a result of climate change often overwhelm antiquated combined sewers that collect stormwater as well as wastewater, while leaky pipes and trash-laden clogs bring stinky backups that can poison local waterways. But as cities scramble to repair and update their networks, another challenge lurks: Getting people to stop taking for granted a public good that’s essential but invisible.