A break Thursday morning in a massive 42-inch water main that supplies Pearl Harbor, off-base Navy housing and the Navy Exchange is affecting tens of thousands of people and has forced the military to institute water conservation measures that could be in place for a week or more, officials said.

“Please limit water use to health and safety purposes only,” Joint Base Pearl Harbor-Hickam said on its Facebook page. “Showers should be limited to short duration. Do not wash personal vehicles. All irrigation of golf courses and yard sprinkler systems will be turned off.”

Three elementary schools closed early Thursday due to the break.

Mokulele, Pearl Harbor Kai and Hickam elementary schools suspended classes, the Department of Education announced. All other public schools in the Pearl Harbor area remained open.

Water was shut off from the Navy’s 42-inch waterline from the Waiawa pumping station after the break was located behind the Pearl City Home Depot, said Chuck Anthony, a spokesman for the base.

“We’re going to backups,” he said, referring to less used waterlines. “So it’s not like we’re without water. It’s just that we have water for a limited duration until they fix that pipeline.”

A small lake formed where the pipe broke, and a 10- to 15-foot sinkhole was reported. A pump was being used to lower the water level, and an excavator with a bucket was scooping out water Thursday afternoon.

The break also affects the USS Arizona Memorial and the three other museums at Pearl Harbor. “They need to conserve water, too,” Anthony said.

The joint base will remain on water conservation measures until the line is completely repaired, which could take a week or more, officials said.

The joint base and Navy properties rely “heavily” on the Waiawa waterline, Anthony said. A limited amount of water was being drawn from the Red Hill and Halawa shafts, he said.

The Board of Water Supply said it was providing supplemental water to the Navy through an existing interconnection in the Manana area.

Residents in military housing reported a loss of water pressure in a variety of neighborhoods.

“Consumers should notice a rise in water pressure throughout the afternoon, evening and overnight as Navy water storage tanks are refilled to capacity,” the joint base said on Facebook. The base assured residents the water is safe to drink.

The expectation was that crews wouldn’t even be able to start excavating to access the break until last night.