In 2007, the use of desalination, the derivation of fresh water from seawater or brackish water, grew by 43 percent globally, according to the Topsfield, Mass.-based International Desalination Association (IDA). In the United States, 65 new plants are planned or under construction, including one in Carlsbad, Calif., which will be the largest in the Western Hemisphere.

Interest in desalination is greatest in areas near the ocean, such as southern California and Florida, but it also is becoming a more viable option for communities where saltwater has begun intruding into freshwater aquifers, says IDA Secretary General Patricia Burke.

Of the 1,416 desalination plants operating in the United States, 53.8 percent are used to filter brackish water, according to IDA. For example, the 27.5 million-gallon-per-day (mgd) Kay Bailey Hutchison desalination facilities that opened in 2007 in El Paso, Texas, treat brackish water to supplement the city's fresh water supply from the Rio Grande.

In southern California, agricultural use strains the Colorado River that supplies fresh water for much of that region and Mexico. That is one reason why Carlsbad, Calif., officials were the first of nine agencies to sign on as customers for a 50 mgd desalination plant that Stamford, Conn.-based Poseidon Resources plans to open in 2011. Water from the desalination plant will reduce the amount the city will need to draw from the San Diego County Water Authority, reducing demand on the Colorado River.

Because the new plant is privately owned and operated, the city has not had to invest any capital in the project. "The citizens are not underwriting the risk of the desal plant, and that's what we wanted," says Jim Elliott, Carlsbad deputy city manager. "What [the desalination plant] gives us is a drought proof source of water [at no extra cost]."

The growth of desalination is linked to the improvement in the quality of the filtration membranes used in the process. The latest membranes are designed to reduce the amount of pre-treatment that is required, reduce the number of times the water passes through filters and last longer than early versions. "Because of the better-quality membranes, the amount of energy used to produce the desalination becomes a lot less, [reducing the treatment's cost]," Burke says.

Catch the Wave

Municipalities make up 68 percent of desalination plant customers worldwide, according to IDA, and the United States is the third largest user of the technology.