HONOLULU -- Frigid waters pumped from the ocean's depths will be used to air condition downtown Honolulu, reducing the state's dependence on fossil fuels while slashing power bills that are the highest in the nation.

The long-studied cooling project by Honolulu Seawater Air Conditioning would extend plumbing nearly 5 miles offshore, suck 45-degree water from 1,800 feet deep and circulate frosty water into buildings' existing A/C systems.

Hawaii's government recently approved an environmental study of the project, and the company said it plans to begin construction next year. The 40-building system is expected to come online in early 2012.

If the $200 million undertaking is successful in downtown, it could later be extended to Waikiki.

Honolulu Seawater Air Conditioning said buildings using the system would save up to 75 percent of the electricity they currently use on air conditioning.