With Southern California rainfall at one of its lowest levels in a century, the agency supplying water to most of the region is calling on consumers to reduce their consumption and has started a radio advertising campaign to get the word out, officials with Metropolitan Water District said Friday.

The "Let's Save" campaign will reach radio listeners across the region starting Monday. It encourages consumers to save water inside and outside the home by doing such things as shortening shower times and reducing the amount of water used in the yard.

Water district officials issued a news release Friday that states that they plan to meet consumer demands for water this summer despite the dry conditions in Southern California.

"However, we understand that every drop of water saved this summer is a drop of water that can be stored for next year and beyond," Metropolitan board Chairman Timothy F. Brick stated in the news release.

To meet demand this year, the agency will have to dip into its reserves to the tune of 500,000 acre feet, Metropolitan Water District officials said. An acre-foot of water is equal to 326,000 gallons, or enough water to supply the household needs of two families for one year.

The region was hit by a six-year drought between 1987 and 1992. But the threat of water shortages was much greater then because the agency only had about 225,000 acre-feet of water stored. Since then, the district has increased its storage capacity significantly and today has more than 2.5 million acre-feet of water stored around Southern California, including Diamond Valley Lake in Southwest Riverside County.

Those reservoirs may come in handy this summer. The Sierra snowpack that helps ensure water supplies for the region was at its lowest level in two decades last winter, state officials have reported.

Concerns have arisen that if Sierra snow falls short again next winter, Southern Californians could face water shortages in 2008. Much of the water from the snowpack flows into the rivers that feed the Bay Delta in the Sacramento area. Southern California's imported water supply comes from two main sources: the Bay Delta and the Colorado River, which is entering its eighth year of drought.

In a Friday phone interview, Metropolitan Water District spokesman Denis Wolcott said the U.S. Bureau of Reclamation considers the Colorado River drought one of the worst in history.

The implications for Southern California are ominous, he said, adding that it's vital that residents learn to conserve.

"If the drought continues for a couple more years, we may have very serious conditions," Wolcott said.

Contact staff writer William Finn Bennett at (760) 740-5426 or wbennett@nctimes.com.