The New York Times noted that the regional water authorities in San Diego have approved a long-debated $320 million desalination plant. From the paper:

"The plant, to be built near Carlsbad, north of San Diego, will be the first large-scale desalination operation on the West Coast and the largest in the hemisphere. 'If they build it well and it operates well and the price is right, we will see more,' said Peter Gleick, the cofounder and president of the Pacific Institute in Oakland, Calif."

Posideon Resources pursued this project for six years. If it succeeds, more could appear on California's coast. The experiment will also likely be watched closely in Australia, which is enduring a years-long severe drought. State governments there are interested in desalination.

When fully built, the plant will filter 100 million gallons of water a day. By 2011, if construction goes as planned, it will spit out 50 million gallons of fresh water.

Besides the environmental concerns, one of the big concerns about desalination is cost and energy consumption. Seawater is pressurized and then shoved through a fine membrane. Some estimates put desalination at $650 to $1,000 or more per acre foot when water agencies often sell water for $200 an acre foot. Put another way, a 25 million gallon a day reverse osmosis plant for seawater can cost $100 million.

So what's the answer? Some, like Oasys (a Yale spin-out) is working on forward osmosis. Rather than shove seawater through a membrane, put a very salty solution on the other side. Seawater will be drawn through under the laws of chemical attraction. No pressure is required to draw the water through and the membrane discharges sea salt. The salty solution on the other side can then be boiled: It is salty because of ammonia molecules that evaporate at low temperatures. 

Others, like Porifera, NanoH20 and Aquaporin sport fancier membranes. Aquaporin, whom we met in Denmark last year, wants to insert synthetic proteins into membranes that will eject salts. The same proteins eject salts in your cells.

Then there is simply better pressure management. Energy Recovery takes the pressure on the waste water streams in reverse osmosis desalination system and feeds it back into the system to pressurize incoming water. They had one of the few IPOs in greentech last year. Unlike Oasys and the membrane companies, Energy Recovery also sells products right now.