Ofwat has published the gate one draft decision on the proposed Lower Thames West London Reservoirs Strategic Resource Option currently being developed by Thames Water to increase resilience in London and the wider South East.
Photo: Queen Mary Reservoir aerial view
Writing to Thames Water CEO Chris Weston on 3 July 2026, Paul Hickey Senior Director – RAPID confirmed that with regard to evidence of efficient expenditure:
- Our assessment of the efficient costs as spent on gate one activities results in a total of £0.129 million.
- Our assessment of the efficient costs as spent on early gate two activities results in a total of £0.449 million. Therefore, under the new combined process, the remaining allowance for gate B is £19.241 million.
The draft decision document includes a list of remediation issues and other steps to be taken in Appendix A divided into priority actions, actions and recommendations.
The assessment has also considered the updated development expenditure templates submitted by Thames Water as part of the gate one submission.
This set out a request for a new gate two allowance of £11.869 million, an increase of £7.764 million, driven by:
- further programme and project management activities
- further design work
- more targeted stakeholder engagement
- further data collection
- further environmental assessments.
However, Ofwat’s draft decision paper states:
“We will not be amending the allowance of £19.690 million for gate B. Solution owners should provide us with a completed expenditure by AMP template following the onboarding of the Technical Partner to allow for a robust forecast, and in line with the combined gated process, to be considered. Priority action 1 has been included to address this.
Reason: A robust forecast for gate B will only be completed once the Technical Partner has been onboarded for this project.”
Following publication of the draft decision, solution owners and other interested parties now have the opportunity to respond to the draft decision. Representations are invited by via a Microsoft Teams form or by email to This e-mail address is being protected from spambots. You need JavaScript enabled to view it - the representation period will close at 6pm on 24 July 2026. Paul Hickey said that all relevant representations will be considered before the final decision, which Ofwat intends to publish on 10 September 2026.
The West London Reservoirs can be divided into two discrete systems which sit north and south of the River Thames. The northern and southern systems are not currently operationally connected, so raw water stored in one part of the system cannot be transferred to the other in the event of a shortfall.
The Lower Thames to West London Reservoirs Strategic Resource Option proposes to develop a new raw water transfer to link the southern and northern reservoirs. The transfer is proposed to be a tunnel, abstracting at Surbiton before running west to the Queen Mary reservoir. The tunnel would also connect to the outlet of the Queen Elizabeth II reservoir to provide a transfer from the southern to the northern reservoirs.
Click here to download the draft decision document
An aerial view of Queen Mary Reservoir
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