Timely update by Paul Rogers in the Mercury News on the largest ocean desalination plant in the Western Hemisphere being built at Carlsbad, which is supposed to supply 7 percent of San Diego County's drinking water when it opens in 2016.

That's about 50 million gallons a day.

The price tag: $1 billion.

Water it produces will cost north of $2,000 per acre foot (about the amount a family of five uses in a year). That's double the cost of water obtained from building a reservoir and four times that of conservation measures such as paying farmers to install drip irrigation.

On the glass half full side, desalination costs less than it used to.

Opponents, including those who object to the huge amounts of electricity the plant will use and the potential harm to sea life from giant intakes at the old Encina Power Plant next door--and who lost in the courts after years of fighting the plant--insist it isn't worth it.

Needless to say, the Carlsbad project will be watched carefully far and wide as a harbinger of desalination efforts up and down the California coast, where a dozen or more such plants (mainly between Los Angeles and San Francisco) are on the drawing boards in coming years.

From the Rogers piece:

The Coastal Commission approved the Carlsbad plant and its open-ocean intake system. But new scientific studies and changing laws mean that most future plants probably will be required to bury intake pipes and pump water at a lower rate to reduce impacts on fish and the millions of larvae, eggs and other sea life that can be killed.

"These organisms become things -- like fish -- and we always have to be careful of the perspective that 'Oh, this is just one little piece,'" said Charles Lester, executive director of the Coastal Commission. "It all adds up."

Image: NBC News