A break this morning in a massive 42-inch water main that supplies Pearl Harbor, 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 days, an official 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 today due to the break.

Mokulele Elementary, Pearl Harbor Kai Elementary and Hickam Elementary suspended classes while repairs are made to the line, the Department of Education announced. All other public schools in the Pearl Harbor area will stay open.

Water was shut off from the Navy’s 42-inch water line 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 lesser-used water lines. “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 in the area.

The break also affects the USS Arizona Memorial and the three other museums in Pearl Harbor.

“They need to conserve water, too,” Anthony said.

The joint base and Navy properties rely “heavily” on the Waiawa water line, Anthony said. For a limited time, there are alternate water sources, including the Red Hill and Halawa shafts, he said.

“We’re using Halawa and Red Hill exclusively until we can get that pipe fixed — and that’s going to take a long time to fix,” Anthony said.

Although water users won’t notice a difference in pressure now, “we still have to conserve water until that pipe is fixed,” he said, “because conserving water buys us more time.”

A lot of water still has not drained from the break site, he said, adding crews won’t be able to start excavating to see where the break exists until tonight.