Even as power is slowly being restored tonight to parts of O'ahu, the Honolulu Board of Water Supply still wants customers to continue to conserve.

"As people get power back on, they're going to think everything's fine," said board spokeswoman Su Shin. "Not true. Without power all day, it will still take time to get the system back up to speed and our reservoirs are getting pretty close to empty."

Depending on how much energy is restored tonight, Shin still hopes that O'ahu's more than 166,000 water customers continue to conserve water through tomorrow morning.

"As far as this happening at any particular moment, it was the best-case scenario," Shin said. "It was raining and (the power outage) happened early in the morning when our reservoirs were maxed out and full."

Without energy, water customers could not use excess water by running their dishwasher or washing machines, Shin said.

Officials recommended people refrain from taking long showers, watering lawns, washing cars and performing other nonemergency tasks.

Water pressure may appear normal at first during a power outage because the water pressure comes from gravity, as water flows downhill from the reservoirs. But as the reservoirs are depleted, the pumps are unable to replace the water.