How worried should New Yorkers be about sewage ending up in city waterways?

New York City is full of peculiar phenomena—rickety fire escapes; 100-year-old subway tunnels; air conditioners propped perilously into window frames—that can strike fear into the heart of even the toughest city denizen. But should they? Every month, writer Ashley Fetters will be exploring—and debunking—these New York-specific fears, letting you know what you should actually worry about, and what anxieties you can simply let slip away.

Every now and again, during a wet and rainy season, the horror stories bubble up and burst forth: Heavy rain in New York City, which in many places drains into the same pipes that direct raw sewage to wastewater treatment plants, causes the whole rainwater-wastewater mixture to flow into the rivers and waterways around the city. This results in some New Yorkers kayaking in other New Yorkers’ toilet water (and some of their trash, which rainwater can also pick up on the streets).

It’s normal—perfectly warranted, even—to worry about city dwellers’ poop contaminating the creeks, rivers, and bays around the city, especially when fecal contamination, according to the environmental nonprofit Riverkeeper, puts any human in contact with the water at risk for several kinds of bacterial and viral illnesses, as well as parasites like giardia.

But how widespread is the problem? What’s the worst it could get? And is there any reason to worry about … the water we drink?

Combined sewers as an infrastructural feature are largely a thing of the past in New York as well as in other cities; as a New York Times story on the subject points out, most water systems built after the 1950s drain wastewater and rainwater separately, with rainwater flowing into waterways and wastewater flowing exclusively to treatment facilities.

The bad news for New Yorkers is that most of New York was built before the 1950s—so “combined sewer overflow” can happen just about anyplace that’s next to a waterway if the weather gets wet enough. The website for the State of New York has a map of every “CSO community,” where residents are advised to “Avoid contact or recreation (swimming, boating, and fishing) within the waterbody during or following rainfall or snowmelt,” and, well, here’s a screenshot of that map:

As the Times points out, though, “only about 20 billion gallons of combined sewer overflows are discharged annually into waterways, down from nearly 110 billion gallons in 1985.” The vast majority of that overflow, too, is rainwater.

That said, if you’re not comforted by the sound of, “Hey, only a little of these 20 billion gallons of dirty water are flushed toilet waste—they’re mostly just germy, garbagey rainwater!” well, fair enough.

The worst years of the potentially disastrous combined-sewer system seem to be, thankfully, behind us. In December 2017, the De Blasio administration released a report that New York Harbor had recently tested “cleaner and healthier than it had been in more than a century,” with bacteria levels dropping and dissolved oxygen levels on the rise.

The mayor’s office credited the city’s massive spending to overhaul the combined-sewer systems: Over the next few years, the city will spend more than $6 billion separating the rainwater and wastewater pipes, adding new overflow-retention tanks and interceptor sewers (and upgrading existing ones), and installing “curbside rain gardens” to create more absorbent space in a city where more than 70 percent of the ground is covered with impermeable surfaces.

Grassroots efforts like the Newtown Creek Alliance, which encourages residents to cut down on sink, shower, toilet, and washing machine use during wet weather, have also inspired the city to work directly with residents to remind them to hold off on using their in-home water systems. Starting in April, residents of neighborhoods in northwest Brooklyn to eastern Queens—where water use during storms can trigger overflows into Newtown Creek, Bowery Bay, Flushing Creek, and Flushing Bay—can sign up (for free) to get these reminders via text message whenever the weather gets stormy enough to potentially trigger a CSO.

As one representative for the New York City Department of Environmental Protection told me, “We do an awful lot of work to reduce sewer overflows.”

Elsewhere in the world, there’s great concern over combined-sewer overflow’s potential contamination of drinking water; in Montreal, for example, researchers investigated this very possibility in 2015. In New York, however, there’s virtually no way combined-sewer overflow could affect the city’s drinking water supply, which flows downstate from three major watersheds north and west of the city, far upstream from the Hudson. It travels through an elaborate system of reservoirs and filtering and treatment facilities, then finally from a reservoir in Yonkers through just three major tunnels and up into our homes, bypassing the city’s waterways entirely.

So that’s one fear assuaged. But as the weather gets warmer (one day, soon, hopefully; please God) and city dwellers start thinking about where to next hop in the water to cool off, it’s of course wise to avoid the areas affected by CSOs. You’re better off swimming only where there’s plenty of tidal flushing—that is, where the water flows out pretty quickly and dramatically—and only when the weather has been dry for a few days.

As a Riverkeeper representative explains, “New York waters can become polluted with sewage for up to 72 hours after heavy precipitation. Yet, contrary to popular opinion, the tidal flushing in areas like the East River, Upper Bay, and Hudson River west of Manhattan often makes those waterways safe for swimming during dry weather conditions.”

Beaches like the Rockaways and Coney Island have also been affected by sewage overflow in the past, such as after Hurricane Sandy. The city often closes those beaches when that’s a concern,but for your own peace-of-mind purposes, you can sign up for the city’s nifty text-message notification system and enable its sewage-spill alert feature.

So on the hottest days this spring and summer, resist the urge to hop in waterways like the Coney Island Creek, which is usually off-limits to swimmers anyway. And whatever you do, just stay the hell out of the Gowanus Canal.

Got a weird New York anxiety that you want explored? E-mail tips@curbed.com, and we may include it in a future column.