Thames Water has updated the design of its proposed White Horse reservoir in Oxfordshire, aiming to secure regulatory approval for the project despite concerns about potential risks. The reservoir, located near Abingdon, would hold up to 150 billion litres of water and cover an area roughly equivalent to the size of Gatwick Airport. The project has grown significantly in scope and cost over the years, with the estimated price now between £5.5 billion and £7.5 billion—more than double the original £2.2 billion. This increase comes after a review last year expanded the site to 38 square kilometers to include additional construction, relocation of solar farms, and the rerouting of local rivers and streams. The project, formerly known as the South East Strategic Reservoir Option, now requires more access points for construction and environmental mitigation, such as creating new habitats. This has necessitated further consultation with landowners and those affected by the changes. A public consultation on the original plans ended in January, and a new consultation has begun, expected to conclude next month. Thames Water aims to submit a planning application by late 2026. If approved, construction could start in 2032, with the reservoir supplying water by 2040 to serve 15 million people. The company says the reservoir is needed to meet the growing population and address the challenges of climate change, which have strained water supplies across the UK, especially during recent heatwaves. Critics argue that Thames Water has underestimated the cost and overstated the project's importance since it was first proposed in 2006. Originally planned as a 10 square kilometer reservoir costing £1 billion, the current design includes walls up to 25 meters high, making it the largest "fully bounded" reservoir in Europe. This is necessary due to the shallow clay layer at the site, which requires the UK’s first walled reservoir structure. Recent cost estimates are based on 2023 prices, and critics say the final cost could be between £7.5 billion and £10 billion, given high inflation in the construction industry. The reservoir has drawn opposition from local councils, including the Vale of White Horse district council, Abingdon town council, and Oxfordshire county council, who have rejected the plans due to concerns about flood risks. Rivers and streams on the site will need to be diverted, potentially increasing the risk of flooding in nearby villages. Campaigners argue that the reservoir is a flawed concept and that more sustainable water supply methods exist. They also criticize Thames Water for inadequate consultation with local communities and for not sharing flood risk assessments, especially since the site is located in a red-rated flood plain—indicating a severe risk of flooding, according to the Environment Agency. Thames Water maintains that the consultation is part of an ongoing engagement process and that feedback will help shape the project’s final design.