The Dream of Desalinization

The prospect of desalination is tantalizing: The Earth’s oceans, after all, hold some 332.5 million cubic miles – that's 1.39 billion cubic kilometers for metric-system folks.

But each gallon in those vast waters holds roughly 130 grams of salt that has to be removed before that water can be drinkable. Removing that salt has always been expensive, prohibitively so, because of the large amounts of energy that it requires to heat the water to extract the salt from it. Reverse-osmosis filtration has been a source of hope for the future, but it, too, is rather energy-intensive: Current methods require between 10 and 14 kWh to produce 1,000 gallons of desalinated seawater, compared with .01 to 1.8 kWh per 1,000 gallons with freshwater treatment.

In Britain, where Thames Water just opened the U.K.’s first desalination plant to make the brackish water of the Thames potable, the process costs twice as much as conventional water treatment. While desalinating brackish water is certainly less energy-intensive than performing the process on seawater – there’s less salt to remove – it is still expensive. And the water also has to be remineralized after it goes through the desalination plant’s reverse-osmosis filters, as they strip out the nutritious minerals in addition to the salt.

The water company’s plans for the plant are to activate it in times of drought and low rainfall, so it functions as a kind of backup in case groundwater supplies are inadequate—as they did in a 2005 drought. Opponents of the plant, however, argue that fixing the leaky pipes that plague any water distribution system would save the same amount of water that the desalination plant will produce, and with less cost and lower emissions.

This move will certainly draw attention to desalination’s potential – but I’m not so sure it’s the backup we should be placing our hope in. Despite the tantalizing idea of desalination, to me water reuse sounds more promising, as soon as we can get over the creepiness factor of drinking water that may or may not have sloshed around the bowl of a toilet.

Indeed, someone in the UV purification sector once shared with me a story about an area in California where his company’s technology was employed to disinfect the water coming from a wastewater plant. After it was disinfected by their UV lamps, he said, the water was 100 percent drinkable. But because the area residents were squeamish about drinking it at that point, the utility re-injected this clean, potable water into the below-ground aquifers. A few miles away, a water filtration plant extracted that very same water, ran it through a filtration system, and sent it out to customers.

What do you think? Will desalination ever become viable? Does water reuse have any potential, or is the “ick” factor still too high?

Posted by Laura Williams on Apr 28, 2011

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