Straws in the Ocean: On Desalination, Water and Climate Change

By Jonathan Marshall

California’s exceptionally low snowpack and the early start to its wildfire season are sobering reminders of how easily the state can succumb to drought. And odds are that we’ll see many  more severe dry spells in the future.

A new study led by NASA warns us that global climate disruption will likely increase the incidence of drought in temperate areas. And the U.S. Office of the Director of National Intelligence reported last year that “Between now and 2040, fresh water availability will not keep up with demand absent more effective management of water resources,” putting at risk the ability of water-short regions “to produce food and generate electricity.”

Desalination plants use lots of energy to create fresh water, but efficiencies are improving. (Photo from Water Corporation/Austalia.)

Recent dry spells, compounded by such gloomy scenarios, explain why no fewer than 17 California communities are seriously considering building desalination plants, with a collective capacity of half a billion gallons per day. (That’s enough for a million people.) Freshwater runoff from the mountains might be in short supply, but the ocean offers unlimited water supplies —for a price.

That price is high — typically $2,000 to $3,000 per acre-foot (the amount of water that would cover an acre to a level one foot high), typically much more than alternatives such as conservation or water reclamation.

Desalination also requires tremendous amounts of energy. As a new report by the Oakland-based Pacific Institute reminds us, using large amounts of energy to turn seawater into drinking water is likely to create more greenhouse gas emissions and compound rather than mitigate our environmental and climate problems.

To produce a million gallons of water from seawater desalination typically requires about 15,000 kilowatt-hours of electricity, equal to the monthly consumption of about 27 typical homes in PG&E’s service area. In contrast, treating wastewater for reuse averages half that amount of energy (or less).

The report’s author, Heather Cooley, notes that compared to desalination, conservation and more efficient use of water are better for the environment, reduce energy use and greenhouse gas emissions, and protect water consumers against unpredictable energy prices. In times of drought, inexpensive hydropower becomes scarce in California, driving up electricity prices and thus the price of desalination.

Cooley notes that the desalination industry is hard at work improving technology, lowering costs, and above all, reducing energy requirements. Current plants use three to four times more than the theoretical minimum amount of energy needed to remove salts from seawater, so there’s plenty of room for improvement.

For instance, GE announced last year that it has developed much more efficient pumps for forcing seawater through membranes to strip away salt. The company promised an overall reduction in energy use of about 10 percent.

That’s a baby step compared to reports that Lockheed Martin Corp., the giant defense contractor, is developing ultra-fine filters for purifying water, using sheets of graphene, a miraculous form of carbon just one atom thick.

“It’s 500 times thinner than the best filter on the market today and a thousand times stronger,” one engineer claimed. “The energy that’s required and the pressure that’s required to filter salt is approximately 100 times less.”

Exciting as that prospect is, let’s not lose sight of more mundane solutions. According to estimates by the American Society of Civil Engineers, old and broken pipes across the United States lose around seven billion gallons of fresh water a day. Maybe we should patch up our existing water infrastructure before dipping too many new straws into the ocean.

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