With water shortages looming in arid regions around the world, many policymakers find desalination plants increasingly attractive. Like nearly any other potential source of drought-proof water, however, desalination plants come with both advantages and disadvantages.
According to a 2009 article from the American Water Works Association, desalination has a variety of both pros and cons. On the pro side, reverse osmosis (RO) technology is reliable and well-understood. If properly designed, desalination plants that use RO can consistently deliver high-quality water to consumers. Even more importantly, the quantity of water stored in the ocean is so vast it's virtually inexhaustible, so desalination is a completely drought-proof source of water.
Desalination is an energy-hungry process. According to a 2008 article in the Ecologist, modern desalination plants typically use around 2 kilowatt hours of electricity to produce a cubic meter of drinking water, and this electricity is often generated using fossil fuels. Desalination plants can often be expensive to build. Moreover, the waste brine from the desalination plant is rich in salt and often contains chemicals like chlorine or anti-scaling agents. Discharging this brine directly back into the ocean can cause local environmental problems.
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Whether desalination is cost-effective for a given community depends on its available resources. As the Water Works Association article notes, social, political and economic factors are often the primary determinants in these kinds of choices. Desalination can help provide a reliable source of drinking water for a community as long as that community is prepared to accept the costs.