Before the end of the year, the backhoes are expected to dig into the dirt on a patch of coastal land in southern California, as construction begins on a massive plant that will draw fresh water from the salty sea. California regulators have given the green light for the construction of the largest desalination plant in the Western Hemisphere in Carlsbad, California, overriding environmental protests. Some green groups are appealing the plant's approval to a state water board, but officials with Poseidon Resources, the development company, seem confident that construction will begin on schedule. When the plant cranks up to high gear, engineers expect it to produce enough fresh water for 110,000 households in the San Diego area.