The £250 million Thames Water Desalination Plant was the first of its kind in the UK. It came into operation in 2010 and can provide up to 150 million litres of drinking water each day, which is enough for nearly one million people.
Much of Thames Water's supply area is classed by the UK Environment Agency as "seriously water-stressed", with customers in London, Swindon and Oxford particularly at risk of water restrictions during extended periods of dry weather.
The plant treats brackish waters – mixed fresh water and salt water – from the river Thames estuary, turning them into clean drinking water. Its prime purpose is to reduce the risk of water restrictions and to ensure severe water rationing is never required during periods of drought or low rainfall.
It runs on 100 per cent renewable energy. It takes water from the tidal Thames during the last three hours of the ebb tide and removes salt using a “reverse osmosis” process. The treated water is then transferred from Beckton in east London via an eight-mile-long pipeline.
The cost of desalination means many countries in northwest Europe deem it prohibitive. The case for solar-powered desalination infrastructure in drought-prone countries is a different matter.
Former London mayor Ken Livingstone dismissed the London plant as a "misguided and a retrograde step in UK environmental policy". He argued it was expensive and unnecessary. Thames Water should instead focus on reducing waste caused by leakage and people should be encouraged "to use less water, not more," he said.
But the Environment Agency now believes desalination has to be part of a range of options in light of increased impacts of climate disruption and population growth.
Recent research by the Crowther Lab in Switzerland backs the agency view. It found London will in the future have the same climate Barcelona has today, and experience more extreme droughts.
Yvette de Garis, head of environmental regulation at Thames Water, stressed recently that desalination was still “very costly both in financial and carbon terms” but necessary for “emergency use”.
Irish climatologist Dr Conor Murphy of Maynooth University says a range of supply options must be considered if the Irish water supply is to be made climate-resilient. But factoring in costs, energy requirements, "brackish outputs" and high carbon emissions, he did not favour pursuing the option in the Irish context.