Environmental campaigners today attacked the government's decision to approve the development of the UK's biggest desalination plant as a backward step in the fight against climate change.
The £200m Thames Water plant at Beckton, east London, will employ an energy-intensive process pioneered in desert countries to convert sea water into drinking water at times of drought.
Planning permission for the plant has been granted by the communities department after a heated inquiry.
The scheme was approved only after Thames Water pledged to use renewable energy to power the plant and to operate it only during droughts or extended periods of low rainfall. It will run on biodiesel, despite growing concerns about the sustainability of biofuels.
The plant will be able to provide up to 140m litres of drinking water a day - enough for nearly 1 million people. It is expected to run for up to 40% of the time over the next 25 years.
Campaigners said approval for the scheme sent out the wrong signals, and said the plant would be unnecessary if Thames Water was better at managing its resources.
Rob Oates, the manager of the UK freshwater programme at the conservation organisation WWF, said:
"It is nonsense to imagine that London, or indeed anywhere in the UK, needs a desalination plant to supply its freshwater needs. This is the UK, not Yemen.
What we really need to do is reduce leakage, which still stands at 25%, introduce universal water metering to reduce demand, end over-abstraction from the UK's rivers and introduce more water-saving devices in homes and businesses.
At the moment, half of the drinking water supplied to homes is used for flushing toilets and washing dirty clothes, which is madness."
Mr Oates dismissed the proposed use of biofuels to power the plant as "an environmental red herring that does nothing more than put a green veneer over a fundamentally damaging project".
The London mayor, Ken Livingstone, opposed the plans during the inquiry. Today, his spokesman said the decision was "a step backwards in the battle against climate change".
The spokesman said the mayor would continue to press Thames Water "to ensure that the environmental impact of the plant is minimised".
Richard Aylard, the director of external affairs and sustainability at Thames Water, said:
"The desalination plant is a vital part of our plans to secure future water supplies to the capital. The plant is essential alongside our continuing progress in reducing leakage and proposals for a new reservoir in Oxfordshire.
It may seem hard to imagine now given the rainfall we've been experiencing, but without this plant there would have been a real risk that Londoners would be facing water shortages in future years."