Thames Water has launched a £5.7bn tender notice to bring a contractor on board to build its proposed nationally significant reservoir in Oxfordshire.

The newly named White Horse Reservoir – previously known as the South East Strategic Reservoir Option (SESRO) - would secure water supply for 15 million people across the South-east, including Thames Water, Southern Water and Affinity Water customers.

Around 1,800 jobs would be created during construction unlocking economic growth and opportunities for business. The reservoir would provide up to 271 megalitres of water per day during drought, the equivalent to around three million baths.

The project is one of nine new reservoirs that would provide water security for the UK, supporting the government's agenda for 1.5 million new homes, unlocking economic growth, and providing long-term resilience against climate change.

The company is now seeking a main works contractor to design, build, test and commission the reservoir which would be situated south-west of Abingdon. The proposed reservoir would supply water locally in Oxfordshire and Wiltshire, through to Hampshire and London.

Chris Weston, CEO of Thames Water, said: “The reservoir represents one of the most significant investments in water infrastructure the country has seen in decades.

“Once built it would be one of the largest in the country, providing water to millions, supporting new homes and development, and creating an exciting new destination where people can unwind and connect with nature. Careers will be made and built through the reservoir’s construction with thousands of jobs created, supporting families and communities across the South-east.”

Chris Taylor-Dawson, senior director for major projects at Ofwat, added: “Kick-starting the procurement process to select the main contractor is a significant milestone in the development of this important project - critical for securing our future water supply in the South-east of England.

 “Building on the success of the Thames Tideway project, using a competitive third-party delivery approach will boost resilience in the sector and deliver better value for customers. Engaging contractors at an early stage in the development of reservoir will tap into specialist expertise and innovative solutions – all of which can help lower costs in the longer term.”

To reflect the heritage and history of the reservoir’s location the company also unveiled the site’s new name, White Horse Reservoir, replacing the name South East Strategic Reservoir Option (SESRO).

Beyond water storage the reservoir will create a place for people and a space for nature.  Once open, it would attract visitors and boost tourism, supporting the regional economy for the longer term.

Roles created during and after construction include ecologists, geologists, archaeologists, engineers, electricians, construction managers, park rangers and sailing instructors.

Feedback gathered during Thames Water’s statutory consultation will shape its reservoir plans and inform its Development Consent Order application, ahead of submission to government later this year. Should the project be approved, water is set to be available for use from 2040.

The main works contractor would build White Horse Reservoir, designing and planning construction, from excavation to building embankments and laying pipelines.

Thames Water is hosting an online applicant briefing on 11 February 2026 regarding the request to participate stage and the main works contract opportunity. Applicants wishing to attend the briefing must register by noon on 10 February 2026.

Details on the tender notice process and how to sign-up to the applicant briefing can on the gov.uk website.

Interested organisations have until 24 April 2026 to submit a request to participate, after which shortlisted, applicants will be invited to submit detailed tenders.