The San Diego agency estimates that the average household bill will increase $5 to $7 a month when deliveries begin in 2016. It figures the cost is comparable to other new, local sources of drinking water.
Poseidon proposed the plant in 1998 and began negotiating with potential customers shortly after the California Coastal Commission approved it in 2009, clearing the last major regulatory hurdle. The company overcame challenges from environmentalists concerned about the plant's massive electricity needs and harm to fish and other wildlife from intake filters and brine that is dumped back into the ocean.
Backers of the project averted a last-minute snag when the city of San Diego proposed shifting costs shift more costs to smaller agencies that don't have their own water treatment facilities. The board agreed to decide later on how the costs will be shared.
"I guess we're going to fight over the next couple years about how all this gets divvied up," said Mark Watton, general manager of the Otay Water District, one of only four agencies that opposed the contract, in part, because it felt the costs will prove higher than expected.
San Diego began to consider desalination in the early 1990s, when a drought led it to conclude that it needed a more diverse, reliable water supply. The agency is also considering giant desalination plants at Camp Pendleton Marine Corps Base and Playas de Rosarito, Mexico, just south of the U.S. border.