Bud Lewis, the mayor of Carlsbad, is a balding, mildly blustery man who has lived in Carlsbad for more than half a century. The Korean War vet and former high school teacher once told an interviewer that his greatest passions are "the love of my wife and family, the love of Jesus Christ, and my love for the city of Carlsbad."

When Lewis moved to this placid stretch of Southern California coastline in 1954, there were 3,000 people here. He was first elected to the Carlsbad city council in 1970 and became mayor in 1986. During his tenure, Carlsbad's population has exploded; today, 103,000 people live on 42 square miles. Fifteen golf-gear manufacturing companies call Carlsbad home, along with 65 high-tech and biotech firms. There are 3,000 hotel rooms in the city, with nine new hotels on the way.

In the early 1990s, growth and drought collided in Southern California, and water use was slashed by up to 30 percent. Lewis began to think seriously about meeting his city's water needs. He was an architect of the city's growth-management plan, which caps the population at 120,000. But stopping growth alone, he says, is not enough to solve the city's water problems. In recent years, Lewis has learned a lot about water; he served on the boards of the Metropolitan Water District of Southern California and the San Diego County Regional Water Authority. And for the last decade, he has also been one of the biggest boosters of Poseidon's desalination plant.

"I told environmentalists that if I had it my way, I would kick all of you people out. But you can't do that. You have to plan for the future. Water is planning for the future. This plant takes care of 10 percent of our water needs, and it is truly a blessing," Lewis says. "But talking about it is one thing and getting it is another."

Lewis put his political muscle behind the plant, even arranging for buses to take dozens of project supporters to public hearings. Poseidon has done its part as well. The company has spent about $595,000 on lobbyists in Sacramento since 2001. And it gave nearly $2,000 to San Diego Mayor Jerry Sanders' 2006 and 2008 election and re-election campaigns. Poseidon is also tied to the San Diego mayor's office through a political consulting firm that has worked closely with both the company and Mayor Sanders.

The proposed plant -- which would pump out 50 million gallons a day, enough to quench the thirst of 300,000 people -- would lie just north of the giant Encina Power Station's dark gray stack. It would suck water from a serene-looking neighboring estuary, Aqua Hedionda ("stinky water" in Spanish) Lagoon, which hosts oyster and mussel farms.

Poseidon's plant would join some 13,000 desalination facilities worldwide, which collectively produce almost 15 billion gallons a day, a number that's growing by about 10 to 15 percent each year. There are over 2,100 such plants in the United States, but they're generally small facilities that treat brackish groundwater rather than ocean water. Together, they provide less than one-half of one percent of all U.S. water supplies.

If the Carlsbad plant is built and its operation proves financially feasible, however, it could open the door to new facilities up and down the coast. As a result, the battle over the plant has become the front line in the nationwide war over desalination.

The company chose a good location to make its stand. Not only is the region thirsty, but Carlsbad is also home to 35 desalination-related companies, employing more than 2,000 people.

"San Diego County is to desalination and reverse osmosis as Silicon Valley is to computer chips," says Peter McLaggan, Poseidon's executive vice president. The company's promotional video says the plant will boost Carlsbad's desalination economy by bringing 2,100 construction jobs, more high-tech and biotech employers and $37 million a year in revenue. It also warns that if the water shortages aren't fixed, thousands of local jobs will be lost.

Flashing back and forth from testimonials to scenes of surf, sand and sun, the video points out that half of San Diego County's residents live less than 10 miles from the ocean, making it a growing market for seawater. And it says Poseidon will dedicate nearly 15 acres around the lagoon to hiking trails, a fish hatchery and beach access.

The video also contains an assurance from Scott Jenkins of the Scripps Institution of Oceanography. A marine engineer who works as a consultant to Poseidon, Jenkins says that "the environmental impacts of these plants have been studied all over the world … providing scientists with a vast body of data which has confirmed that these plants do not harm the marine environment."

Finally, the video explains that the plant's filters will remove impurities so small they can't be seen by the naked eye. "The membrane converts sea water into two streams: ultra high-quality drinking water and concentrated sea water, which is then mixed with sea water leaving the power station to the ocean. The entire process takes 20 minutes."

Perhaps. But getting a plant built and running properly -- even in Carlsbad -- will take much, much longer.