four more desalination plants, but this has not progressed. Operation The plant takes water from the Tideway during the last three hours of ebb, storing the water in a reservoir to minimise the salinity of the water processed. The water is first treated by a conventional settlement and filtration before the salinity is removed by reverse osmosis. Mineral salts, as found in the company's conventional water sources, are added before final purification. The plant is intended to be used during times of low natural water supply and exceptional demand. The operating license dictates that the plant can only be operated if required by Thames Water's drought management plan, when the river flows at Teddington are less than 3000 megalitres per day. It can also be used in operational emergencies. In 2022, some industry sources said the plant had been effectively mothballed because of high running costs. It was not used in the very dry conditions of summer 2022 because of "necessary planned work". Criticism London Mayor Ken Livingstone criticised the plant in 2007, calling it a "misguided and a retrograde step in UK environmental policy." Livingstone, arguing that the plant was expensive and unnecessary, said that Thames Water should instead focus on reducing waste caused by leakage and that people should be encouraged "to use less water, not more." Livingstone blocked the plans as “unnecessary and unsustainable”, but it was given approval when Boris Johnson became mayor in 2008. References Desalination plants in the United Kingdom Desalination Plant Water supply and sanitation in England and Wales Beckton