SAN MARCOS ---- Vallecitos Water District officials said Monday they are interested in buying potable water from a Connecticut-based company that is planning to build a desalination plant in Carlsbad.

"It's a new local source of (water) supply," Vallecitos General Manager Bill Rucker said. "It has tremendous opportunity."

The company, Poseidon Resources, is planning to build a $270 million desalination plant that will be able to produce 50 million gallons of potable water a day. The city of Carlsbad plans to purchase up to 25 million gallons and the company is looking to sell the remaining 25 million gallons to other water districts in the county. Carlsbad officials said the plant is expected to open in 2008.

One of those districts interested in purchasing the water is Vallecitos, an agency that serves 76,500 customers in San Marcos, parts of Carlsbad and Escondido, and some unincorporated parts of the county.

Rucker said he has met with Poseidon officials on several occasions to discuss a possible purchase. Talks are preliminary right now, he said, adding that a deal is far from being reached.

Rucker said the company needs to establish a price for the water, determine how it will be delivered from Carlsbad to San Marcos and determine how much it plans to sell. Vallecitos, he said, is considering buying between 5 and 15 percent of its daily water supply from the desalination plant.

Poseidon officials did not return calls for comment.

The water district currently gets 60 percent of its water from the Colorado River and 40 percent from the Sierra Nevadas, water that is brokered through the San Diego County Regional Water Authority. The regional water agency charges $522 per acre foot of water ---- equivalent to 326,000 gallons of water ---- to 23 water districts, cities and Camp Pendleton, said Ken Weinberg, the agency's director of water resources.

Carlsbad officials said they have agreed to buy water from Poseidon for 30 years at a price that is equal to or less than the county water authority is charging when the plant begins operating in 2008. Under the contract, the desalinated water's price will not exceed what the water authority is charging for 30 years after 2008.

Jim Elliott, the city's administrative services director, said it will be cheaper to buy desalinated water because it will eventually cost more to treat and deliver imported water. Weinberg said the water authority's rate is expected to nearly double, from $522 to $960, in 12 years.

If Vallecitos ends up buying water from Poseidon, Rucker said the district may save money in the long run.

"If (regional water authority officials) stay on the plan to double the wholesale cost, certainly the desal plant is competitive down the road," he said.

Rucker said the desalination plant is a reliable water supply, because unlike the Colorado River and Sierra Nevadas, desalinated water would not be affected by drought. Also, the quality of desalinated water is better than river water because it is treated at a higher level, he said.

Betty Ferguson, president of the Vallecitos water board, said she supports purchasing water from Poseidon as long as the price is reasonable.

"I think anytime you can find an alternative source of water and not be dependent on imported water, it is something you should look into," she said.

Contact staff writer Ken Ma at (760) 761-4408 or kma@nctimes.com.