Regulators approve next phase of Reservoir plans in Abingdon 2026

Key Points

• Regulators have advised that Thames Water’s proposed Abingdon reservoir is ready to move to the next stage of development, unlocking further preparatory work and funding.
• Thames Water has opened an 11‑week public consultation on the scheme, with submissions informing a planned Development Consent Order (DCO) application expected in autumn 2026.
• Cost estimates for the project have risen from earlier figures; current estimates range between £5.5bn and £7.5bn, with internal modelling suggesting around £6.6bn.
• The reservoir is proposed as the South East Strategic Reservoir Option (SESRO) to supply up to 271 million litres per day and to benefit around 15 million customers served by Thames Water and neighbouring suppliers.
• Regulators, including the joint body formed by Ofwat, the Environment Agency and drinking‑water regulators, have stressed scrutiny of value‑for‑money, demand forecasts and alternative options.
• Thames Water aims for the scheme to be ready for construction by 2029 and in use by about 2040, subject to securing consents and financing.

Abingdon(Oxford Daily)May 14, 2026. Regulators have concluded that the proposed Abingdon reservoir is sufficiently mature to move into the next stage of development, enabling further design work, funding and preparation toward a Development Consent Order (DCO) expected later this year or in autumn 2026; the company has also opened an 11‑week public consultation to gather views that will inform the DCO application.

What has prompted regulators to move the Abingdon reservoir to the next stage?

As reported by New Civil Engineer, the Regulators’ Alliance for Progressing Infrastructure Development (Rapid) — the joint body formed by Ofwat, the Environment Agency and drinking‑water regulators — has advised that Thames Water’s proposal has reached a level of maturity that justifies progression to the next development phase, which unlocks further public funding and technical appraisal.
Thames Water has stated that the next steps will allow detailed option appraisal, environmental assessment and procurement planning ahead of a DCO submission, and that the current public consultation will feed directly into that application.

What is the scale and purpose of the reservoir?

The scheme, named the South East Strategic Reservoir Option (SESRO), is planned as a nationally significant piece of infrastructure designed to bolster long‑term water supply resilience for London and the south‑east, with an ability to deliver up to 271 million litres a day and to serve roughly 15 million customers across multiple water companies.
Thames Water has framed the reservoir as a strategic response to drought risk and future demand, intending the facility to be operational by about 2040 if consents and procurement proceed on the current timetable.

How much will the project cost, and how has that changed?

As reported by Thames Water and covered by national outlets, recent detailed design work has produced a more refined cost range for the Abingdon reservoir, which now sits between £5.5bn and £7.5bn, with an internal estimate cited at approximately £6.6bn — a significant revision from earlier, lower public figures.
Regulatory commentary has emphasised close examination of the project’s value‑for‑money case, instructing scrutiny of cost assumptions, demand forecasts and potential alternatives such as enhanced demand management or other supply options.

What consultation and planning timetable has been announced?

Thames Water launched an 11‑week statutory consultation to gather public and stakeholder views, with the company saying feedback will directly inform its DCO application, which it expects to submit to the Secretary of State in the autumn of 2026.
Company representatives have indicated that advancing to the next development stage is intended to ensure the project is ready for procurement and construction planning, with an ambition to start enabling works ahead of a main construction phase around 2029, subject to consents.

What concerns have been raised by regulators and other observers?

Regulators have explicitly asked for tighter evidence on value‑for‑money and have signalled that they will interrogate the reservoir’s demand forecasts and cost basis as part of the next‑stage checks.
Media coverage and public reporting have noted local and national interest in environmental impacts, land‑use implications and the balance between large new storage infrastructure and alternatives, such as leakage reduction and demand management measures.

Who stands to be affected by the reservoir?

Thames Water and the two named partner companies that would benefit from the storage, including Affinity Water and Southern Water, among others in the supply area, say the scheme would provide resilience for millions of customers in the south‑east and London.

Local communities, environmental groups and landowners around Abingdon have been identified in consultation materials as parties with direct interests in routeing, ecology, landscape and construction impacts; the ongoing consultation is the formal route for such stakeholders to register views and concerns.

What are the next steps and likely outcomes?

With regulators’ endorsement to move the proposal forward, Thames Water will proceed with more detailed design, environmental assessment and procurement preparatory work supported by additional public funding and regulatory oversight; consultation outcomes will be collated and used to refine the DCO application expected in autumn 2026.
Regulators will continue to scrutinise the business case, and ministerial decision‑making on any DCO will follow statutory examination procedures, during which objectors and supporters can make representations.

Background of this development

Thames Water first proposed a major strategic reservoir in the south‑east as a long‑term measure to increase storage and drought resilience, with initial public discussion and earlier cost estimates published before detailed design work was completed.
Public consultation rounds have previously been used to shape routing, environmental mitigation and community engagement, and the regulator‑led Rapid forum was created to coordinate assessment of nationally significant water infrastructure to ensure consistent scrutiny of planning, environmental and delivery risks.

Prediction — how this development can affect customers, regulators and local communities

If the project proceeds through the DCO process and secures consent, customers in the south‑east could see improved long‑term water security, reducing the risk of supply restrictions during extreme drought periods, though any direct consumer bill impacts will depend on regulatory determinations and cost‑sharing arrangements.
Regulators will face continued pressure to balance demonstrable value‑for‑money and environmental protection with infrastructure delivery; local communities may experience prolonged construction‑phase impacts and will use consultation and examination stages to seek mitigation and compensation measures.