Developers of a proposed $270 million desalination plant here began gathering public comments yesterday on what it should include in its environmental impact report.

The report is a precursor for permits that Poseidon Resources, a Connecticut company with offices in San Diego, needs before it can build at the Encina Power Plant.

About 50 people attended the session at the Carlsbad Faraday Center.

Bob Size, a retired industrial contractor, said he wanted to know how the plant would work.

"This explains most of it," said Size, 73, pointing to a giant diagram of seawater being transformed into drinking water.

The plant could produce up to 50 million gallons of drinking water per day, enough for up to 300,000 people.

The Encina location is important because the Poseidon technology needs to work in tandem with the power plant. The desalination process, through reverse osmosis, would remove salt from the water used to cool the power plant's generators.

Several people wondered if the environmental impact report, or EIR, will consider what could happen to the desalination plant should the power plant cease operation.

The EIR "needs to study the possibility the (desalination) plant would have a life beyond the power plant," said Marco Gonzalez of the Coast Law Group, which represents several environmental agencies.

Cabrillo Power, owner of the power plant, has no intention of leaving the area, said David Lloyd, the company's secretary.

The Encina Power Plant meets about 25 percent of San Diego County's energy needs and will be around for the "foreseeable future," he said.

City planner Scott Donnell said the EIR will not include a scenario without the power plant. A draft of the report should be ready next summer.

Construction on the desalination plant would not begin until 2006 after Poseidon has secured permits from the state as well as a land- use permit from Carlsbad and an ocean-discharge permit from the Regional Water Quality Control Board.

The plant could begin delivering water in early 2008, the company said.

Carlsbad could purchase all of its water -- up to 25 million gallons per day -- from the plant. Poseidon also is pitching its plan to other cities to see how big the first phase of the plant needs to be.

"I'm worried about the financial arrangements," said Renata Breisacher Mulry of Carlsbad.

She expressed concern her water bills would increase if the city entered into a contract that might result in higher costs for repair and distribution.

Poseidon has quoted a price of $900 per acre-foot, including distribution fees of $100 per acre-foot.

Water from the County Water Authority costs cities much less. Carlsbad pays $530 per acre-foot and San Marcos $550 per acre-foot, including distribution fees.

The Metropolitan Water District, however, might offer a desalination subsidy of $250 per acre-foot to encourage new water sources. The County Water Authority, however, has not committed to transferring the subsidies it could receive to any cities or agencies purchasing water from Poseidon.