From the Guardian
Mar 31, 2010
The world's unquenchable thirst for clean water drove a record increase in the desalination and reuse of sewage last year, figures show, as water-stressed countries around the world try to build their way out of trouble.
Making fresh water from the sea was once the preserve of cruise ships and oil-rich
that could afford the huge cost of energy required to remove the salt. But as rivers, lakes and aquifers dry up, rains become less reliable, and the cost of desalination falls, communities in all parts of the world have begun to build and plan plants to turn oceans, estuaries, salty ground water and even sewage into clean water for factories, farms and homes. Gulf states
The rise in fresh water production was the biggest ever recorded, reaching 9.5 cubic metres a day, the annual report by analysts Global Water Intelligence will say tomorrow. That is equivalent to twice the annual flow of the
Thames, or about 10% of global capacity. Those desalinating and reusing water include some of the poorest countries, including Algeria, India and . Ghana
But wet overpopulated cities such as
London and are also investing in the technology. Dublin
With water "manufacturing" allowing people to change fundamentally the geography of fresh water on such a large scale, Christopher Gasson, GWI's publisher, talks of "rivers flowing backwards".
"People do desalination when they run out of opportunities, and the problem is the world overall is running out of opportunities: groundwater is overexploited to the extent it's becoming saline and unusable; rivers are being drained; new dams are becoming less and less viable [and] long-distance transfer is expensive and controversial,"he said.
The fundamental reason for the rise of water manufacturing is a simple gap between demand and supply: in 2006 a report from the International Water Management Institute found one in three of the world's population were "enduring one form or another of water scarcity" – such as "when women work hard to get water, [or] you want to allocate more but can't".
Growing numbers of people, richer lifestyles, demand for water-intensive food such as meat, and dwindling supplies are expected to increase that number – to up to half the projected global population or more in the middle of this century. And that is despite an expected doubling of water manufacturing capacity between now and 2016, according to UK-based GWI.
The falling cost of desalination, thanks to technology improvements, is key, and the reuse of water can be cheaper still.
Contracts have been signed to deliver desalinated water in Algeria and Israel for 55–56 cents (36p) a cubic metre, and reuse plants can now turn sewage into drinking water for 40–45 cents a cubic metre, said Gasson. To compare, the average cost of
drinking water is about 51p a cubic metre, though that also includes piping the water to the tap. UK
Comparisons between the energy needs of different desalination methods – heating up water for distillation or pushing it through membranes to filter the salt – have also become much closer. Continuing developments in membranes – which one day are likely to be modelled on the "technology" nature uses in kidneys and mangroves – will continue to bring down costs and energy needs, said Gasson. Systems using carbon-free energy are also being tested: nuclear desalination in the UAE, solar power in
Australia, and biodiesel from plants at a desalination plant built by Thames Water in . London
Despite the advances, there are still serious objections to manufacturing water. The WWF remains concerned about building facilities in often environmentally sensitive coastal and wetland areas; about the intake of seawater, which is home to millions of tiny species, and discharge of the remaining brine, which can be contaminated with cleaning chemicals and particles from corroding pipes. Concerns about the energy use of plants also still remain, especially where they are still dependent on fossil fuels, or if they could divert renewable resources which could otherwise replace existing carbon-intensive energy supplies. Residents in upmarket
, have long objected to a desalination plant being built there because they fear it would encourage more development. Monterey, California
The capital, surrounded by desert, has the world's only system that treats waste water and puts it back into the public water supply, mixed with water from the city's main reservoir. The success of the scheme is credited to a long-standing public acceptance campaign, including advertising, education in schools and an "excellent" water-quality record.
Arizona and Nevada, US: desert desalination
North American states and
Mexico share the Colorado river under a treaty signed in 1922. It has been suggested Nevada funds a desalination plant in return for more of 's river water. into the river, allowing upstream towns and cities to keep more of the fresh flow. Mexico
Despite its rainy reputation,
London receives less rainfall than Rome, Dallas or . To cope with an expected 800,000 more residents by 2016, Istanbul Thames Water has built a desalination plant next to its Becton sewage works.
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About the author
Juliette Jowit is the Observer's environment editor.