White Horse Reservoir (formerly SESRO)
Thames Water wants to build a very large new reservoir on farmland south-west of Abingdon, west of the A34, between Steventon, East Hanney and Drayton. For years it was known as the South East Strategic Reservoir Option (SESRO). In 2026 Thames Water renamed it White Horse Reservoir, saying the new name reflects its local setting and heritage.
What is proposed
The reservoir would be enclosed by embankments and filled with water taken from the River Thames in winter. In dry periods the water would be released back into the river to be taken out again downstream, supplying customers of Thames Water, Affinity Water and Southern Water. Thames Water says it would serve around 15 million people. The plans include floating solar panels, new wildlife habitats, paths, water sports and visitor facilities, and a diverted Hanney to Steventon road.
By the numbers
- 150 billion litres of storage
- Up to 6.7 km² in area
- 2029 to 2040: forecast construction period
- 17 construction access points, up from 6
A long and contested history
A reservoir here was proposed before and rejected by the government in 2011 after a public inquiry. The land has nevertheless been safeguarded in the Vale’s local plans, with the council stating its objection. The scheme returned in regional water plans and was included in Thames Water’s Water Resources Management Plan, approved in September 2024. In January 2025 the Chancellor listed it among water projects the government supports.
Costs have been a major point of dispute. Oxfordshire County Council quoted a figure of up to £1.4bn in 2022. The Vale says the scheme was costed at £2.7bn when the 2024 plan was approved, rising to £6.6bn in Thames Water’s 2025 submission to regulators, and “up to £7.5bn” was reported in August 2025. Both councils oppose the reservoir. They argue that fixing leaks, water recycling and transfers from other regions would be better, and they have raised concerns about safety, flood risk, carbon emissions and a decade of construction.
Where it stands
Thames Water held its statutory consultation from October 2025 to January 2026, and more than 1,200 people attended its nine events. It has since dropped a plan to move three existing solar farms and increased the number of construction access points. As a nationally significant infrastructure project, the reservoir needs a Development Consent Order from the government, not local planning permission. Thames Water expects to apply in late 2026, and the Planning Inspectorate will then examine the scheme.
How to follow it
Follow the project on Thames Water’s White Horse Reservoir page and the Vale council’s SESRO page. Once the application is submitted, people can register to take part through the Planning Inspectorate’s national infrastructure website.