With population growing and fresh water resources running dry, desalination seems like the perfect solution to the world's increasing thirst. Just take some sea water, or brackish water from an underground source, and remove the salt. What could be simpler?
In principle, the process really is that simple. The salt is removed either through evaporation or by forcing the salty water through filters. But it takes a lot of energy and, depending on how it's produced, the end result could be more greenhouse gas emissions or nuclear waste.
Under pressure from environmentalists, Australian engineers are using wind energy at a new desalination plant in Perth. James Duggie of the World Wildlife Fund (WWF) in Western Australia is equally firm about a second project. "If there is to be a desalination plant, it should be zero emissions in terms of greenhouse gas emissions and it shouldn't cause environmental impacts when it's established," he says.
Worldwide, desalination plants have been built where energy is affordable. It's no surprise that more than half of all seawater desalination plants are located around the Arabian Gulf, where cheap oil and water shortage come together. Nearly all the remaining plants are in countries rich enough to pay the energy bills--such as Spain and the U.S. The U.S. has the world's second-largest desalination capacity.
Energy is not the only environmental impact of desalination. In the case of sea water plants, there's the risk of sucking in marine organisms along with the water, and all desalination plants produce extremely salty water as waste. If this is thrown back in the sea undiluted, the salt concentration is lethal for most sea creatures. Solutions exist to minimize these problems--but at a price.
What are you going to pay for your glass of desalinated water? Costs at the plants range from $700 to $1,160 per acre foot, not including distribution costs. Desalinated water is generally more expensive than natural fresh water, at least while the latter remains available for exploitation. Looking at the costs another way (for membrane-filtered water) energy makes up nearly half of the cost, with around 40 percent going to fixed charges (repaying the original investment) and the rest on daily operations and maintenance.
Cost benefits are in some cases marginal or non-existent, so why is there such an interest in desalination projects at the moment, particularly at a time of rising energy prices...