Main Works Contract for White Horse Reservoir
Thames Water Utilities Ltd has launched procurement for the Main Works Contract (MWC) for the newly renamed White Horse Reservoir (formerly SESRO). The project forms one of the UK’s largest strategic water‑resource investments, designed to secure long‑term drought resilience across the South East and deliver major environmental and community benefits.
The reservoir—a fully bunded, non‑impounding raw water storage facility—will be located south‑west of Abingdon, Oxfordshire, with an operational capacity of 150 million m³ and a water surface area of 6.7 km². Water will be abstracted from the River Thames and conveyed to the reservoir via a pumping station and approximately 4 km of tunnels.
Procurement Structure
The MWC procurement comprises:
A multi‑supplier Framework Agreement, and
A single Call‑Off Contract based on NEC4 ECC Option C, incorporating X22 Early Contractor Involvement (ECI) and bespoke amendments.
The Call‑Off Contract follows a two‑stage ECI model:
Stage One: design development, construction planning, secondary consents, Target Price confirmation.
Stage Two: detailed design, construction, testing and commissioning (subject to Notice to Proceed).
At the end of Stage One, the contract will be novated to the Infrastructure Provider (IP), a new regulated entity established under the Specified Infrastructure Project Regulations (SIPR)—the same model used for the Thames Tideway Tunnel.
Scope of Works
The MWC will deliver the full design, build, test and commissioning of the reservoir and associated infrastructure, including:
Tunnelling and pipelines: reservoir tunnels and river tunnel.
River Thames intake/outfall, including a sheet‑piled cofferdam.
Reservoir earthworks: embankments, borrow pit excavation, replacement flood storage.
Watercourse diversions, floodplain works and drainage.
Temporary rail siding and materials handling area on the Great Western Main Line.
Pumping station, reservoir towers and major concrete structures.
Road construction, including overbridges and access routes.
Mechanical and electrical systems, utilities diversions and power supply.
Ancillary buildings, visitor facilities and operational structures.
Landscaping, habitat creation and long‑term land management.
Enabling works: site clearance, demolition, archaeological and environmental surveys, geotechnical investigations, boundary security.
The project includes passive design provisions for future integration with wider strategic water‑resource and flood‑alleviation schemes, including the Thames to Southern Transfer (T2ST) and Farmoor Transfer.
Programme
• Estimated contract period: 11/08/2027 – 31/03/2043
• Reservoir operational target: 2040 (filling may take several years)
• Visitor facilities and landscaping: continuing to 2043
Regulatory & Technical Oversight
The project is being developed in full compliance with the Reservoirs Act 1975. A Construction Engineer and Reservoir Advisory Panel are appointed to oversee design, construction, first filling and early operation.
Estimated Value
• £5.7 billion (excl. VAT)
• £6.84 billion (incl. VAT)
(Values at Q2 2025 prices; inflation excluded.)
Client:- Thames Water Utilities Ltd, in partnership with Affinity Water and Southern Water.
Further information: (thames-sro.co.uk )
Notice ID: 2026/S 000‑005547
OCID: ocds‑h6vhtk‑060bb3
Published: 22/01/2026
Submission address and any special instructions
https://www.smartsurvey.co.uk/s/WHR_MWC_APP_BRF_REG/
This link will take interested parties to the Applicant Registration Form. Completing the Applicant Registration Form will then, subject to confirmation, provide suppliers with access to the secure site containing the Procurement Specific Questionnaire Pack (PSQ Pack) and submission portal.
For further information please visit https://www.find-tender.service.gov.uk/Notice/005547-2026 05/26.
