A major water main break on Farrington Highway threatened to shut off water to nearly 13,600 Leeward Coast residents last night, but as of 10 p.m. there were no reports of any homes without water service.

Residents living between Ali'inui Drive and Hakimo Road — from the Ko Olina Resort area to the edge of Nanakuli — were expected to feel the brunt of the water shortage.

Officials urged Leeward residents to continue to conserve water today because a major reservoir in Wai'anae that provides water to the other communities was nearly depleted. It will take a while to replenish that reservoir, Board of Water Supply spokeswoman Su Shin said.

"We're strongly urging Leeward Coast residents, from Barbers Point to Makaha, to limit water use to essential use only — drinking, cooking and personal hygiene," Shin said.

The leaky 44-year-old main broke yesterday morning and forced a shutdown of one of two town-bound lanes just after the Ali'inui Drive on-ramp at Ko Olina. Shin said last night that the repair work was expected to be completed by this morning, but possibly not in time to allow all lanes to be opened for rush hour traffic.

Shin said water trucks were dispatched to Nanakuli High School and in front of the Waimanalo Gulch Landfill office on Farrington Highway to provide aid for the likely shortage. Several other roaming trucks were also expected to be in the affected areas, she said.

Late last night Shin said there were no requests for the roaming trucks and water was still available. She credited the Leeward community's response to a request for conservation, as well as Board of Water Supply crews that diverted water from Wai'anae to the Lualualei area.

"People are really good about that. When we ask for conservation, they respond to that," Shin said.

The damage to the 24-inch main was on the underside of the pipe and crews needed to excavate and remove water from the deep hole before they could begin their repair work, Shin said. Before crews could get to the leak, the highway's asphalt had cracked and water had been seeping out, Shin said. The break occurred about 50 feet past the Ali'inui on-ramp and was reported just after 7 a.m. yesterday.

Leeward-bound traffic was unaffected.

"It's real difficult (to know the cause of the break)," Shin said. "It can be a number of things — corrosion, movement in the soil."

Nanakuli resident Dennis Sakamoto had water as of yesterday evening, but wasn't thrilled about the potential shutdown.

"(Nighttime) is the worst time," Sakamoto said. "It's when everybody gets home for cooking and showering."

The water problems raised concern among officials because of recent fires on the Leeward Coast. Firefighters rely on hydrants when fighting blazes near homes and other property, said fire Capt. Kenison Tejada.

"If there's no water service we will have to use tankers and the water that's already on the truck, which is about 500 to 750 gallons," Tejada said.

Depending on the number and size of the hoses used, 500 gallons can last as little as two minutes to as long as a half-hour, he said.

"We have enough water to cover for a little while, the homes and stuff like that, but not indefinitely, not if it's a big fire," Tejada said.

Ken Williams, vice president of operations for the Ko Olina community association, said the resort will do whatever is necessary to comply.

Water main breaks "are not planned things. ... Hopefully we (will) manage through it," he said.