Environmental costs of desalination
Improvements in technology coupled with the rising costs and decreasing reliability of traditional water supplies are leading water-short cities to look to the oceans for drinking water. Despite its popularity, the process of removing salt from seawater to make drinking water is so energy intensive, however, that the resulting greenhouse-gas emissions could contribute to regional water scarcity, according to a global survey [PDF size: 4.8 MB] of desalination plants by environmental group WWF.
"An awful lot of electricity is chewed up to desalinate this water, and that electricity, if generated from fossil fuels, will exacerbate the greenhouse effect," says Jamie Pittock, who is a director of WWF's global freshwater program and is a report author. Climate change may also be responsible for erratic weather patterns such as drought, which creates even more water scarcity.
Recent industry statistics estimate that worldwide desalination capacity will increase 61% between 2006 and 2010 and a total of 140% by 2015 to 97.5 million cubic meters of water per day. Most of the growth in capacity will occur in the Middle East and northern Africa, but capacity will also increase in China, India, Australia, Spain, the U.S., and even the U.K.
The trend toward more and larger desalination plants raises issues about climate change, "although it's not clear what the relative importance of desalination is versus every other greenhouse-gas-emitting activity," points out Heather Cooley, a senior research associate at the Pacific Institute, an environmental think tank. She also listed increasing greenhouse gases as a possible negative environmental effect from desalination in a report [PDF size: 1.5 MB] she wrote on California's market.
A larger concern, Cooley points out, are the as-yet unknown long-term effects of several ecological impacts. For example, numerous tiny marine organisms are killed as they get sucked up into a desalination plant. And the plants produce a brine byproduct laced with chemicals, such as coagulants, antiscalants, biocides, and detergents, used in the treatment process, for example, to prevent membrane fouling. The brine waste is typically discharged directly into the ocean.
The WWF report stresses that in most cases, other options—including conservation, more efficient water use, and recycling wastewater—would provide the same benefits as desalination, at lower economic, social, and environmental costs.
Wade Miller, executive director of the WateReuse Association, an industry group, agrees that desalination isn't a panacea. "Every major water utility needs to look at the whole portfolio of water supply options and see where desalination fits in," Miller says. He adds that his organization is working in conjunction with others to fill research gaps raised by the WWF report.
