Falls Lake Dam was built to control flooding on the Neuse River. There is room to store more water for Raleigh residents behind the dam, but as a precaution, rain from Hanna is going to flow down stream.
Falls Lake is Raleigh's main water source.
Currently, water fills about one-third of the reservoir's total capacity.
Raleigh continues to order water restrictions on 400,000 area residents.
But if Hanna drops a lot of rain over the Triangle, much of the water that flows into Falls Lake will be released down stream.
"The water will be released from the lake as soon as possible in case there's a second hurricane," Raleigh Mayor Charles Meeker said.
The Federal Army Corp of Engineers decided how much water to release and when. In the past, Meeker has asked the Corp to store more water during dry months.
"Certainly we'd like to see the lake a little bit above normal in the April/May/June timeframe when there might be a drought when the hurricanes are very unlikely," Meeker said.
But now, in hurricane season, Meeker agrees with the Corp that Falls Lake should not be allowed to rise above normal.
"There's no question that having a lot of water and having it go down stream is frustrating," Meeker said. "But we have to live with the size of the lake we have. But some of that water will recharge the ground water, which will refill the lake over time."
And as far as water restrictions are concerned, Meeker said the Triangle can expect permanent water rationing.