Many Hawaiian Electric customers on Oahu turned out their lights and went to sleep Wednesday night before knowing whether the utility had to implement rolling blackouts around 10 p.m.

The possibility of forced outages rotating around parts of the island was announced by the company at about 2 p.m. based on supply and demand estimates after an unexpected shutdown of the largest independently owned power plant on the island, a 208-megawatt facility operated by Kalaeloa Partners.

Initially, Hawaiian Electric warned of possible outages starting at 6 p.m. and lasting 30 minutes to an hour for different parts of the island at different times during evening peak power usage.

But the company was able to bring back online a generating unit at one of its own power plants that was down for scheduled work to make up for some of the potential shortfall.

“Previous demand forecasts predicted insufficient generation earlier in the evening, but Hawaiian Electric crews were able to ramp up additional generation resources at Kahe Power Plant and expect that large-scale battery storage will help provide power to all customers through the evening peak,” the company announced at about 5 p.m.

Uncertainty over whether rolling blackouts would be necessary was largely due to the uncertainty of demand.

Hawaiian Electric has about 310,000 customers on Oahu, from small households to hotels and other large businesses. The company asked all customers to reduce their use of electricity, especially during the peak evening hours from 5 to 9 p.m.

The Kalaeloa Partners plant shut down at around 1 a.m. Wednesday due to the rupture of an underground pipe necessary for operations, according to Hawaiian Electric. Repairs to the plant, the utility added, could take three days.

“Until those repairs are complete, rotating outages during times of peak demand may be necessary and customers are being asked to reduce their use of electricity, especially during the evening,” Hawaiian Electric said before the Kahe Power Plant generating unit added to the supply of energy.

The Kahe plant is the largest on Oahu, with a capacity of 650 megawatts from six generation units.

The last time there were rolling blackouts on Oahu was in January, when about 120,000 customers in more than two dozen communities throughout Central, Leeward, East and Windward Oahu had their power purposely cut off for up to roughly 30-minute periods that began shortly before 8 p.m. and rotated around the island until shortly after 10 p.m.

January’s incident was triggered mainly by two of six generation units at Hawaiian Electric’s Waiau Power Plant in Pearl City being knocked offline in a storm. The two units combined had a 100-megawatt production capacity at the 500-megawatt plant. One unit was flooded and the second unit lost its transmission line to the grid.

Other contributing factors to the January outages were less solar energy generated and stored in batteries during the bad weather, less wind power at the time and reduced generation by the city’s HPOWER garbage-to-­energy plant.

Hawaiian Electric implements rolling blackouts to prevent bigger outages on its system when demand outstrips supply.

In response to the initial warning by the utility Wednesday, the Honolulu Board of Water Supply announced that it planned to reduce its electricity usage by pumping less water, and therefore asked customers from the Leeward Coast to Kahala and Mililani to begin conserving water immediately.

“BWS customers are being asked to conserve water and use only for cooking, drinking, and personal hygiene,” the agency said. “Please hold off on non-essential uses such as car washing, watering plants and lawns, and doing laundry until further notice.”

If Hawaiian Electric had to implement outages Wednesday night, a rotation by area was planned in the following order:

>> Waipahu, sections of Pearl City, Kunia, Ewa Beach

>> Waiawa, Crestview, Mililani, Kunia, Waimalu, Upper Kipapa region

>> Pearl City, Waimalu

>> Majority of Leeward Oahu

>> Lower Kalihi, sections of Upper Kalihi

>> Kakaako

>> Sections of Kahala

>> Sections of Kaimuki and Kapahulu

>> Majority of Kaimuki, sections of Kapiolani Boulevard and Waikiki

>> Manoa

>> Nuuanu and School Street

The company said downtown Honolulu, Chinatown and Hawaii Kai were excluded due to recent large outages in those neighborhoods.

Roughly 20,000 customers in Hawaii Kai were without power early Tuesday morning, and roughly 490 waited until Wednesday morning for power to be restored after work was completed on underground cables.