Ocean Water Desalination: Our Next Source of Drinking Water?
The Tampa Bay Desalination Plant produces 25 million gallons per day of fresh water from seawater using 9,600 of these reverse osmosis membranes. Courtesy of Poseidon Resources.
The $350-million Carlsbad desalination plant near San Diego, California, broke ground late in 2009. Courtesy of Poseidon Resources.
The U.S. is already produces 1.6 billions gallons of water a day from desalination. The country’s largest desalination plant in Tampa Bay, Florida began operations in December 2007 and produces 25 million gallons per day. The plant’s developer has two additional desalination plants under development in California. In San Diego, the regional water authority is planning to supply 10 percent of the region’s total water supply requirements through local seawater and brackish groundwater desalination by 2020.
There are two basic ways to remove the salt from seawater: either distill it as steam from brine or separate the salts from the freshwater through a reverse osmosis or electrical process. In a desalination process, salt water is separated into two parts: one that has a low concentration of salt, essentially drinkable, and the other with a much higher concentration than the original feed water, usually referred to simply as “concentrate.”
At about $900 to $1,100 per acre-foot (one foot of water covering one acre of land, equivalent to about 326,000 gallons), costs for desalinated water are 30 percent or more than conventional sources in California, and the electricity to produce 1,000 gallons costs about $1.10. Given those figures, it’s far cheaper to conserve water than to provide new supply. Conservation and efficiency are always going to be cheaper than new infrastructure solutions.
Although building new desalination plants should be a last alternative for solving urban water supply needs, I think desalination will be part of our 21st-century water future because it’s one of our few drought-proof resources.
Learn more about desalination in Chapter 13 of my new book, Dry Run: Preventing the Next Urban Water Crisis, published in June 2010 by New Society Publishers.
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