"Water, water everywhere, / Nor any drop to drink." ---- Samuel Taylor Coleridge, "The Rime of the Ancient Mariner," 1798.

Coleridge's sailor could have been describing the coastal desert that is San Diego County. But this week, the county's first major effort to separate salt from the sea to provide drinking water cleared its first regulatory hurdle. We join the Carlsbad Planning Commission in cheering on the desalination plant proposed by Poseidon Resources Corp., a major step toward sustainability in a thirsty region.

On Wednesday night, Carlsbad's planning commissioners voted unanimously to approve the Poseidon project, which could someday pump 50 million gallons of drinking water a day ---- or 8 percent of the county's water demand ---- out of the Pacific Ocean. The next step is a hearing before the Carlsbad City Council, expected to come in June. The step after that ---- the California Coastal Commission ---- will likely be where the project's pace slows to a trickle.

That's because the desalination project is still drenched in questions. For one, who will ultimately own and operate the plant is still in negotiations. While Poseidon is applying to build the nearly $300 million facility, the Connecticut-based company is still talking to the San Diego County Water Authority about a possible transfer to the authority. If that sale goes through, the application approved Wednesday night ---- which would have Poseidon own the plant and sell its product to the city of Carlsbad and the Valley Center, Olivenhain and Rincon del Diablo water districts ---- might no longer hold water.

Another concern is the project's effect on the marine plants and animals that will be killed as water is sucked from the sea. The good news is that no new water would be drained from the ocean for the Poseidon plant. The facility, which is planned for a 4-acre site at the Encina Power Station next to the Agua Hedionda Lagoon, would use only seawater already being sucked up to cool the power plant. That's a good thing, too, because the state Lands Commission this week banned any new plants from drawing any more water from the ocean.

The project's symbiosis with the Encina power plant raises another question. The aging plant, owned by NRG Energy Inc., has long been an eyesore that fouls North County's air more than more modern energy-generating facilities. There's some concern that the desalination project could give Encina a new lease on life just when North County might want to begin foreclosure on the polluting practices of the past.

But these concerns are less important than San Diego County's urgent need for new, reliable sources of drinking water. North County has had many reminders of the vulnerability of our water supply in recent years. The five-year droughts preceding the last two wet winters starved the Northern California snowmelt that supplies Southern California with 60 percent of our water. A radioactive pile of slag in Moab, Utah, threatens the Colorado River, which supplies more than a third of San Diego County's drinking water. Soaring populations in Nevada, Arizona and Colorado lobby to lower California's share of the Colorado. The water bottleneck through the R.A. Skinner Treatment Plant near Temecula can't keep pace with the growing population; much of North County came close to seeing taps turned off in late 2005 due to expansion work being done at Skinner.

The main knock against desalination has always been the cost; water was always cheaper to get in less energy-intensive ways. But technological advances, much of them made right here in San Diego County, have made desalination an increasingly affordable prospect.

The Poseidon project is a major step toward a more secure water supply. North County, so long accustomed to looking north and east for our water, must begin to look west.