Desalination has been regarded as too energy intensive and expensive for public water supply in the UK. But that myth is now being overturned by two companies facing short-term supply shortages.
Thames Water says it is already operating a one megalitre per day pilot plant on the Thames estuary. It plans to apply to the London Borough of Newham this summer for planning permission to build a £200 million full-scale plant producing enough water to supply 900,000 people.
A company spokesman said: "We're planning to use a four-stage reverse osmosis process featuring energy recovery, which is considered the most energy-efficient way of treating seawater. We also plan to take water from the river just below low tide, when it is least salty, which will mean lower energy costs."
The plant will produce up to 150 megalitres of drinking water a day and discharge saline effluent into the estuary. The proposed site is next to the company's massive Beckton sewage treatment works.
The plant is primarily intended to meet peak summer demand in the London area. Thames Water has a severe water shortage in the area and it needs more resources to satisfy its regulators that it can meet demand in the event of a severe drought.
Peter Spillett, Thames' environment and quality manager, said that the costs of desalination had come down in recent years: "We have the technology and the costs are affordable".
The plant will be built by Pridesa, a Spanish company acquired by Thames' parent company RWE in 2002. The company has extensive international experience in reverse osmosis desalination technology, having built 50 plants in Spain, Portugal, Italy, South America, Egypt, Turkey and China.
Mr Spillett described the desalination scheme as "an accelerated resource management project". The project comes against a background of the company's struggle to control leakage in the London area and no agreement in sight on plans to develop a new reservoir in the Thames Valley.
An Environment Agency report into companies' resource plans last November criticised Thames over its projections on leakage and its failure to plan an increase in water metering (ENDS Report 346, pp 13-14 ). The company is currently proposing a massive mains replacement programme as part of its business plan for 2005-10.
Thames says that per capita water consumption is increasing. It expects London's population to expand by 800,000 by 2016.
However, Thames may be pipped at the post in bringing the first desalination plant on line. South East Water is also constructing a pilot plant at Newhaven, East Sussex. If all goes to plan, it will complete a smaller 9.5Ml/d plant in 2006-07.
Supply demand manager James Grinnell said that the plant, costing less than £10 million, was needed to boost supplies at times of low river flows, such as last summer. The plant would add around 5% to the company's daily water supply of 400Ml/d.
Desalination plants are becoming a key option to resolve peak water supply shortages. Eight companies, including Thames and South East, included desalination proposals in their draft water resources plans submitted to the Agency last year.