CARLSBAD, Calif. — There’s far more riding on the Americas’ largest seawater desalination plant than the 50 million gallons of drinking water it will produce for the San Diego area each day.

The plant, which opens this year, will help determine the future of seawater desalination in the U.S. The billion-dollar project is only the nation’s second major seawater plant. The first U.S. foray in Tampa Bay is widely considered a flop.

The desalination plant opening this year in Carlsbad, Calf., is the largest in the United States. Desalination supporters say it is a partial answer to drought in the U.S., while opponents say it threatens marine life and costs too much. The Associated Press

“You have to be able to say we did it there, it worked there,” said Peter Beland, North America editor for Global Water Intelligence, which tracks the industry.

Supporters consider seawater desalination a partial answer to drought in the U.S. Opponents say high costs and threats to marine life leave better alternatives, like recycling and conservation.

Huge by U.S. standards, Carlsbad barely cracks the International Desalination Association’s list of 50 largest seawater plants, which are mostly in the Middle East. Its Israeli designer modeled it on one in Tel Aviv that produces nearly three times the water.

Tampa, which has half the capacity of Carlsbad, opened in 2007, a decade after it went to bid. Along the way, a key investor declared bankruptcy, its replacement failed to secure financing and the plant repeatedly failed performance tests.

San Diego County Water Authority officials vowed to “Tampa-proof” their effort, tapping experienced builders and getting developer Poseidon Resources LLC to shoulder much of the risk. In return, the Boston-based company will get a 9.66 percent return on investment, even more if it hits certain targets.

The plant uses a well-proven technology called reverse osmosis, which uses powerful pumps to shoot ocean water through 2,000 white fiberglass tubes to capture salts. First, silt and other solids are removed to prevent membranes from clogging – a task that hobbled the Tampa plant. Treated water is pumped uphill on a new 10-mile pipeline to San Diego’s existing grid.

“Each element, each building block of the plant is something that has worked before elsewhere,” said Avshalom Felber, chief executive of IDE Technologies, the plant designer. “That wasn’t the case in Tampa.”

San Diego began considering desalination in the early 1990s when drought exposed dependence on water brought hundreds of miles from Northern California and the Colorado River. It picked Carlsbad, a prosperous suburb of 110,000 people, because it could draw water from a power plant next door that uses up to 600 million gallons from the ocean daily to cool turbines.

Under a 30-year agreement, the regional agency will pay up to $2,367 an acre-foot, more than double what it will pay to import water next year from the Metropolitan Water District of Southern California. (An acre-foot supplies two typical households for a year.)

The San Diego agency says the plant will provide about 8 percent of the region’s drinking water and raise the average monthly household bill about $5. Bob Yamada, its water resources director, said desalination “is not going to be a silver bullet that solves all of our problems” but has better positioned the region for drought.

Poseidon is pursuing an identical-size plant in Huntington Beach, California, a Los Angeles suburb.

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