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Amazon says its new headquarters in Long Island City, Queens, will bring 25,000 jobs. It will also bring more crowds, more noise and, yes, more toilet flushing.

It might seem mundane, but what happens in the bathroom matters: New York, for all its modern conveniences, sits atop a century-old sewage system used by more people than ever before. Every time someone flushes, washes their hands or takes a shower, all that household wastewater (and worse) flows down into 7,500 miles of sewer pipes. Most of these pipes also do double duty, collecting rainwater runoff from rooftops as well as streets.

When these sewer pipes get clogged by humans — flushing baby wipes anyone? — or simply overloaded with rainwater, it becomes everyone’s problem. The “combined sewer overflows” are discharged directly into nearby rivers, bays and creeks instead of going to wastewater treatment plants. Raw sewage also backs up in homes, creating a stomach-turning mess.

Long Island City residents say these backups and overflows already happen whenever it rains hard — and 25,000 more Amazon workers will only make the problem worse. But city officials say they are ready to take on whatever comes down the pipes. Here is why.