“Pride” of the city, New York tap water may taste different

New York’s tap water — a source of pride for residents — may taste a little different for a while.

This week, a pristine watershed in the Catskill Mountains that supplies about 90% of the city’s drinking water will be temporarily reduced by half, while a less-utilized source will make up the difference.

A portion of the Delaware Aqueduct, responsible for providing about half of the city’s water, will close for eight months for critical repairs, resulting in the loss of an essential water source: the Delaware portion of the Catskill-Delaware watershed, which encompasses five rural counties in New York State. This basin represents the largest source of unfiltered water in the United States.

However, there is a contingency plan: another river basin, which provides around 10% of the city’s water but is normally reserved as backup, will compensate for part of the shortage. Officials said this means New York’s water, while still safe, may deviate from the taste residents are accustomed to as the city completes crucial repairs to its water infrastructure.

“Just as different brands of bottled water taste a little different, so do our different basins,” said Rohit T. Aggarwala, commissioner of the Department of Environmental Protection, which oversees the city’s water supply.

The nearly century-old Delaware Aqueduct is 82 miles long and runs from the Catskills region, north of New York City, to the city’s main reservoir in Yonkers.

In the 1990s, leaks were discovered in a 2.5-mile section of the aqueduct near Newburgh, New York, about 70 miles north of the city, and at another location further north. The tunnel was losing up to 132 million liters of water per day.

With the closure of this part of the Delaware Aqueduct, the goal is to bypass the leaky section by connecting the aqueduct to a new tunnel, construction of which was completed three years ago. This final phase of the aqueduct repair project, which cost US$2 billion, is expected to take eight months.

The city’s other water source, which will make up for the shortage during repairs, is known as the Croton watershed, and its water is not as clean as that of the Catskill-Delaware watershed. This is due to the fact that Croton is closer to developed areas in suburban counties north of New York City, meaning its water contains more drainage and disposal. Croton water must be filtered, according to the Environmental Protection Agency.

In 2015, the Croton Water Treatment Plant opened in the Bronx. During the eight-month closure, the station will increase its operations but will only be able to produce about a quarter of what the city needs daily.

To make up the difference, some of Croton’s unfiltered water will be mixed with water flowing from the Catskills, in a ratio of approximately 1 to 3, and directed to the city’s main reservoir.

The technique, called “blending,” can be controversial, said Sarah Meyland, a water expert based in Huntington, New York. “If you are mixing high-quality water with lower-quality water, the concentrations will be diluted in the supply,” he said. “But that doesn’t mean you won’t have exposure to whatever is in Croton’s water.”

It’s likely that microorganisms commonly found in many watersheds could appear in the unfiltered mix of Croton and Catskill water, Meyland said. However, Paul Rush, deputy commissioner of the city’s Department of Water Supply, said all water, whether filtered or not, is tested and treated for pathogens and other contaminants with chlorine and ultraviolet light.

A recent report on the repair project cited “episodic taste and odor issues” in the Croton system’s water, which were being closely monitored. While the plant in the Bronx can treat Croton water using a carbon filtration process, the Catskill-Croton mixture will rely on simple dilution to do the job.

Rush said water from all the basins and treatment plants serving New York would eventually combine in the pipes that supply the city, further diluting any changes in taste or odor.

There’s also a technical problem with the Bronx filtration plant, said Bob Cooney, a retired quality engineer: It doesn’t have backup power for its pumps.

Rush stated that in the event of a power outage, the system would continue to operate using gravity alone. “We analyze all contingencies,” he said.

Meyland, who followed the early planning phases of the Delaware Aqueduct closure, said that relying more on the Croton watershed was a sensible and necessary approach, given that water demand in and around the city averages about 3 billion liters per day.

But she acknowledged that restructuring the city’s water system remains a significant technical challenge: “It’s a little uncharted territory.”