All electrical power has been restored across O'ahu, and the water reservoirs are now running at 100 percent, Hawaiian Electric Co. and Board of Water Supply officials said this morning.

HECO crews worked overnight to restore power to a handful of homes that had been without power since the islandwide blackout occurred shortly after 6:30 Friday night when a thunderstorm passed through. Most of HECO's 293,000 customers had power restored last night.

"We had power back for most customers by 8:30 last night, but we had 125 pockets — no specific areas — where crews had to work from 8:30 last night to 6:30 this morning to restore power," said Peter Rosegg, HECO spokesman.

Rosegg said cause of the islandwide blackout is still undetermined and an investigation will start Monday. More information may be released this afternoon, Rosegg said.

Su Shinn, BWS spokeswoman, said O'ahu's water reservoirs were nearly 100 percent filled this morning and that no residents should be without power or have low pressure. On Saturday, BWS officials were urging conversation because the power outage drained the more than 200 reservoirs across the island.

"Except for a pocket in Kuli'ou'ou, our reservoirs are filled," Shinn said. "Everything should be back to normal. Customers shouldn't feel any effects."

Shinn credited O'ahu residents with making the conservation efforts a success.

"People heard our calls to conserve and actually conserved," Shinn said. "What we were fighting was trying to pump water back into the reservoirs while people were still using and need water. That's why conservation was so important. We're very grateful to the public for their conservation efforts."