New York City’s tap water — a source of pride for residents — might taste a bit different for a while.

This week, a pristine watershed in the Catskill Mountains that provides about 90 percent of the city’s drinking water will be reduced by about half, temporarily, and a lesser-used supply will make up the difference.

A chunk of the Delaware Aqueduct is closing down for critical repairs for eight months, resulting in the loss of a core water source: the Delaware portion of the Catskill-Delaware watershed, which encompasses five rural counties in New York State. The watershed represents the largest unfiltered water supply in the United States.

But there is a contingency plan: Another watershed, which supplies the city with about 10 percent of its water but is typically reserved for backup, will make up some of the shortfall. Officials said this means that New York’s water, though still safe, might deviate from the taste residents are accustomed to, while the city completes the crucial repairs to its water infrastructure.

“Just like different brands of bottled water taste a bit different, so do our different reservoirs,” said Rohit T. Aggarwala, the commissioner of the Department of Environmental Protection, which oversees the city’s water supply, in a statement.

The nearly century-old Delaware Aqueduct is 85 miles long and extends from the Catskills region north of New York City to the city’s main reservoir in Yonkers.