In a move that should eventually ease looming threats of drinking-water shortages in San Diego County, regional water officials in Los Angeles Tuesday voted to spend $91.9 million to expand the R.A. Skinner water treatment plant near Temecula.

Board members for the Metropolitan Water District, Southern California's main water supplier, approved the multi-million dollar expenditure -- of which San Diego County ratepayers will pay about 25 percent -- as expected Tuesday.

San Diego County water officials have been warning local residents that they could face mandatory water cuts on hot summer days for two years because of Skinner.

They say the region's population has outgrown the peak capacity of the Skinner plant -- which provides about half the treated water San Diego County uses annually.

The plant began to fall short of meeting peak water demands for short periods in 2002. However, the predicted water cuts have not materialized.

Even so, San Diego County Water Authority officials say county residents will face the possibility of summertime water cuts for the next two summers -- until the Skinner expansion is completed Jan. 1, 2007. In August, Water Authority officials asked county residents to voluntarily reduce outdoor watering to stretch supplies.

"We're very pleased that they took this action; it will help alleviate some of the treated water constraints we've been having the last few years," said Gordon Hess, the Water Authority's imported water director.

The Skinner plant was built in 1976 to serve San Diego and southwest Riverside counties. The plant's capacity has been expanded three times before. But its capacity has been outstripped by the booming population growth in the last decade.

The plant can now churn out 495 million gallons of drinking water per day. The expansion would increase capacity to 600 million gallons per day.

While Water Authority officials welcomed the Metropolitan action Tuesday, they also said the Skinner expansion would only be a temporary patch for the county's treated water shortage problems.

They said even with the expansion, population growth would again quickly outgrow the plant's capacity.

To deal with that, the Water Authority plans to build its own treatment plant -- the first in its 60-year-history. The proposed $103 million plant is expected to be built by 2008, probably in Twin Oaks area of San Marcos.

"We really need to do both," Hess said. "That (Skinner) will help for a couple of years, but we need to have our treatment plant online … that will get us through the next several years."

San Diego County has historically relied upon Metropolitan to supply nearly all the water it gets. At the same time, because the Water Authority has never built its own treatment plant, county residents have come to rely heavily upon Skinner for drinking water.

Some Water Authority member agencies -- the cities of San Diego, Escondido, Oceanside, Poway, Ramona and Encinitas -- have small water treatment facilities.

But they have limited treatment capacities and there are no pipelines connecting those smaller facilities to other agencies and cities in the county.

Contact staff writer Gig Conaughton at (760) 739-6696 or gconaughton@nctimes.com