Southern California's largest water supplier is set to raise rates to offset higher electrical bills, protect endangered fish and pay for cleanup associated with an invasive mussel.

Board members of the Los Angeles-based Metropolitan Water District are expected to approve what amounts to a 14.3 percent increase for its water in March, officials said.

If approved, the increase means that the typical household could pay about $1.50 more a month, said Bob Muir, spokesman for the Metropolitan Water District. It would take effect Jan. 1, 2009.

Metropolitan is the region's main water provider, selling water to nearly 18 million Southern Californians in six counties - including Riverside and San Diego - through 26 member cities and agencies.

Brian Thomas, Metropolitan's chief financial officer, said the cost of supplying Southern Californians with water was going up, and would continue to go up for the next several years, for several reasons, including:

• Rising electrical costs: The price of the power needed to pump water from Northern California over the Tehachipi mountains and to Southern California continues to increase.

• Fish: In August, a federal court issued a ruling to protect Northern California's tiny Delta smelt, which could limit available water supplies. Thomas said Metropolitan was having to buy increasingly expensive water from farmers and water banks to hedge against the looming shortages.

• Mussels: Last year, Southern California's water systems were invaded by a fingernail-sized mussel, the Quagga mussel, which was costing Metropolitan millions of dollars in cleanup costs. Quagga populations can multiply rapidly and clog pumps and equipment, as well as foul reservoir water supplies.

Water officials in Riverside and San Diego counties said they blanched when they saw the proposed rate increases.

Just a year ago, Metropolitan board members approved a 5.8 percent rate increase, which was the agency's largest rate increase in more than a decade.

"It's very troubling," said Randy Record, a board member with Eastern Municipal Water District, which serves customers in parts of Southwest Riverside County.

Thomas said the proposed increase was actually 9.8 percent, plus a $25 per acre-foot surcharge, which penciled out to the 14.3 percent hike. An acre-foot of water is 325,900 gallons, enough to sustain two households for an entire year.

Jim Bond, an Encinitas councilman and longtime San Diego County Water Authority board member, said many people might not notice the increase.

That is because water is cheaper than other utilities, such as electricity, and because Metropolitan's wholesale rates make up only a portion of Southern California ratepayers' bills.

However, the Metropolitan increase could eventually prompt the agencies that buy its water, such as the Water Authority, and, in turn, local retail agencies to increase their own rates.

"But when you think that an average family uses half an acre-foot of water a year," Bond said, "that $25 per acre-foot is not an egregious amount."

However, Bond, Record and Metropolitan officials said they expect rates to continue to increase.

Metropolitan officials said they expect a cumulative 25 percent to 30 percent increase by 2011.

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