Water, Water Everywhere, So Let's All Have a Drink
Offshore desalination could turn the oceans into an inexhaustible water supply.
by Patrick Huyghe
With a recent government study projecting that at least 36 states will face water shortages within the next five years, some states are looking to tap our oceans for more than a trickle of our freshwater needs. The only significant seawater desalination, or desal, facility in operation in the United States is the Tampa Bay Seawater Desalination Plant, which after a problem-plagued start is finally producing 25 million gallons of water a day, or about 10 percent of the region's water supply. California, Texas, Massachusetts, and Georgia are all cautiously considering similar saltwater desal plants. But critics say (pdf) these plants are energy hogs that have a hugely detrimental impact on coastal marine life.
One potential alternative that’s getting a lot of attention these days, not just in the United States but around the world, is the idea of offshore desalination platforms or vessels. “There are so many obstacles and hurdles to overcome in building and running a desal plant onshore,” says Charles “Skip” Griffin, a senior vice president with PBS&J Engineers who has been designing water-treatment plants for 40 years, “that going off-land is kind of a no-brainer.”
Offshore, the water can be extracted from an optimal depth where sea life density is low and where the water is cleaner, reducing the extensive pretreatment that onshore plants must perform. Furthermore, the concentrated saltwater left over after processing can be more thoroughly diluted in the deep ocean rather than being dumped near shore, where marine life is plentiful. And the cost of powering an offshore plant is expected to be less than for land-based plants; while land-based plants end up having to buy third-party power, an offshore plant could produce its own without the markup.
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