It is becoming a much more credible alternative and that is a good thing.
Published online 19 March 2008 | Nature 452, 260-261 (2008) |
Water: Purification with a pinch of salt
Climate change, growing populations and political concerns are prompting governments and investors from California to China to take a fresh look at desalination.
Quirin Schiermeier
Water has always been a volatile topic in Australia, the world's driest inhabited continent, but the political row that broke out last week was perhaps surprising. Protesters are complaining that a planned desalination facility outside Melbourne, Victoria, will generate too much freshwater.
The US$3-billion government-owned plant will produce more than 300,000 cubic metres of drinkable water a day when it opens in 2011, putting it among the world's biggest. Environmental groups claim that the plant is unnecessary. Even if water consumption rose by 25%, there would be an excess of about 60% in supply over consumption by 2016, according to Neil Rankine, a spokesman for protest group Your Water Your Say. Rankine's figures are based on the state increasing other efforts such as recycling water and harvesting rainwater.
Nobody, of course, is actually worried about the possibility of having too much water — at issue is the cost to the environment. “Desalination is the most energy-intensive form of water supply,” says Peter Gleick, president of the Pacific Institute, an independent environmental think-tank in Oakland, California. The Victorian plant will sit next to a six-turbine wind farm, but few believe that the small, inefficient farm will be able to power the huge facility. The highly concentrated brine discharged by the desalination processes is also of ecological concern.
The economic payout is steep too. Unlike the mass production of other consumer goods, there is no pronounced economy of scale at play in 'making' water — even massive plants cannot produce desalinated water at significantly lower costs than small, community-based facilities.
Increasingly, countries are willing to pay the price. Nations from Australia to Britain, the United States to China, have desalination projects in the works — 75 major plants are at various stages of development globally (see graph, right). Currently, more than 40 million cubic metres of desalinated water are produced every day by 15,000 or so production facilities worldwide. “In the next 10–20 years we will see a massive increase in capacity and production,” says Bruce Durham, an independent consultant who has worked with the water industry for more than 30 years. In California alone, proposals have been put forward for at least 20 new large desalination facilities (see map), which together could ultimately supply some 6% of the state's urban water demand.
Costs have come down. Even the very energy-intensive thermal plants in the Gulf region — which purify seawater by boiling and condensing — can produce fresh water at less than US$1 per cubic metre. And the desalination plant at Ashkelon in Israel, once the world's largest, produces more than 300,000 cubic metres of freshwater per day at costs of around 50 cents per cubic metre. That's 1,000 litres of drinking water for less than half the retail price of a 1-litre bottle of Evian. But on average, the technique is 3.5 times more expensive than using other sources of freshwater such as pumping from aquifers.
