The $1 billion Carlsbad Desalination Plant, the largest in the Western Hemisphere, is adjacent to the Encina Power Station on the Agua Hedionda Lagoon and produces 50 million gallons of purified water daily, enough to supply 400,000 San Diego County residents. This pic shows part of the interior of the reverse osmosis building, which contains more than 2,000 pressure vessels housing more than 16,000 reverse osmosis membranes.

link to more info