Thames Water redraws White Horse reservoir plan and opens a new consultation

A revised footprint

Thames Water has amended the land and access plans for its proposed White Horse reservoir near Abingdon, Oxfordshire, and opened an additional public consultation. The above-ground project is designed to store 150 billion litres of water across a surface area of about 6.7 square kilometres. The latest changes add access points and land needed for construction, river diversions and environmental mitigation, including the creation of replacement habitat.

The supplementary consultation follows a broader statutory process that ended in January. Thames Water expects the new round to close in October and aims to submit its development-consent application later in 2026. If approval and financing remain on schedule, principal construction could begin in 2032, with water entering service around 2040 for customers of Thames Water, Affinity Water and Southern Water.

Why the project matters

The reservoir is intended to address long-term pressure from population growth, climate change and increasingly unreliable seasonal supplies in south-east England. Government planning identifies the project, previously called the South East Strategic Resource Option, as the largest reservoir proposal in current English water-resource plans. National monitoring released in September also showed reservoir storage continuing to decline during an unusually dry year, reinforcing the strategic case for additional capacity.

The economics are far less settled. Estimates have increased from roughly £2.2 billion to a range of £5.5 billion to £7.5 billion in 2023 prices. Critics argue that inflation and construction complexity could push the eventual total higher. Customers of the three participating water companies are expected to finance the asset through bills over many decades, making cost control and regulatory oversight politically consequential.

Local councils and campaigners object to the scale of the fully bounded structure, whose containing walls could reach 25 metres. Their concerns include flood modelling, dam-breach planning, water quality, biodiversity, traffic, river diversions and disruption during a construction programme lasting much of the 2030s. The government’s reservoir-safety programme confirms that raised reservoirs fall under a dedicated legal and inspection regime, but project-specific assessments still have to be tested through planning.

What to watch

The immediate issue is whether the targeted consultation materially changes the design or merely documents objections before the application. Regulators must also decide how the project will be financed and delivered, and whether competitive procurement can protect customers from further escalation. The planning examination will have to reconcile a measurable national water-security need with local safety evidence, environmental impacts and credible alternatives such as transfers, recycling, leakage reduction and demand management.