New York City’s drinking water may regularly be compared to champagne, but for the next few months, it might contain earthy and musty notes instead of its usual pristine bouquet. But officials say there is no reason to be alarmed—the funky flavor, while unpleasant to some, is harmless.

The reason is a shift in where New York City gets its water. As part of a long-term project to repair aging infrastructure, officials have shut down the Catskill Aqueduct, a 92-mile-long tunnel that provides about 40% of the city’s drinking water.

The Catskill water system is one of three networks of reservoirs scattered around western New York and the Hudson Valley that offer water to the five boroughs. The Delaware system provides half of the city’s supply, while the Croton system makes up the final 10%. Only residents of Manhattan and the Bronx are served water from the Croton Reservoir, since it was completed decades before Brooklyn, Queens, and Staten Island were consolidated into New York City.

But with the Catskill Aqueduct shut down for repairs, the Croton reservoir is picking up the slack as it has during past repair projects, said Adam Bosch, a spokesman for the New York City Department of Environmental Protection.

“Whenever the city relied more on Croton water, we would always get a day or two of water quality calls from people,” Bosch said. “And it's really because Croton water has always tasted different than the water from the Catskills.”

Located about 22 miles from NYC, the New Croton Reservoir was placed into service in 1905. It replaced the original, much smaller Croton Reservoir, which was NYC's first upstate water supply and went into service in 1842.

NYC Water via Flickr

That’s because a water supply’s source affects its flavor. Generally speaking, Bosch said water from the Croton Reservoir has a more mineral taste because it is built on top of limestone rock. The geology of the Catskill Mountains is different, so a consumer experiences a different mouthfeel.

“We did a little taste test internally amongst DEP employees, and there's actually a lot of people who prefer the taste of the Croton water,” Bosch said. “I actually was one of them.”

However, since the current repair project on the Catskill Aqueduct began in 2018, officials noticed that the phone calls during periods where they relied more on water from the Croton Reservoir were becoming more frequent—and weren’t stopping after just a few days. Some New Yorkers reported musty flavors in their tap water, similar to the smell after raking leaves. Others experienced that scent of the woods after a fall rain. When officials tested the water, they found elevated levels of a pair of naturally occurring compounds that have caused similar tastes and odors in other drinking water systems around the world.

“Sensitive people can actually detect these organic compounds in concentrations as low as 10 parts per trillion, which is equivalent of 10 grains of sand in an Olympic swimming pool, or the equivalent of a pinch of salt on 10 tons of potato chips,” Bosch said.

The compounds, methylisoborneol (or MIB) and geosmin, are products of microbial activity and organic decay -- germs feasting on dead wildlife. Bosch said they will likely start appearing in water from the Croton Reservoir in the next few weeks and could remain for a month or two. While unpleasant to some Dr. Kartik Chandran, a professor of environmental engineering at Columbia University, said they typically appear in late summer around Labor Day when water temperature rises.

“These are relatively harmless. We don’t need to reorient our [water] treatment technologies to target each and every compound,” said Chandran.

As the Catskill Aqueduct celebrated 100 years in service in 2015, many DEP employees began work to rehabilitate the cut-and-cover portions of the aqueduct for the first time since it was built.

NYC Water via Flickr

Even though the three water systems are surrounded by all manner of plants and wild animals, the off-flavors can be more prevalent in water from Croton because its reservoirs are smaller and warmer than the others, making it more hospitable for microbial life. Factor in climate change, and it could become even more common during future fall seasons. And Dr. Chandran said New Yorker tastebuds could experience the same again this time next year, when the city plans to shut down the Delaware Aqueduct to make major repairs.

Still, it’s understandable that tap water suddenly tasting different would be concerning for some. Despite well-intentioned warnings from city officials, Brian Rahm, director of Cornell University’s New York State Water Resources Institute said it’s natural for people to be uneasy about changes in their water.

“You always run the risk, of course, when you give the explanation that the explanation itself makes people freak out because they're throwing in some of these words that most people don't run into as part of their normal life,” said Rahm

In the meantime, if your water tastes weird, city officials recommend calling 311. While that may not provide instant relief, Bosch said refrigerating the water or adding flavors like lemon juice can help cut the off-flavor.