Our five-year plan from 2025 to 2030

2026 Cost change process

As part of the PR24 Final Determination, Ofwat set up a framework for schemes where scope, costs or delivery were uncertain at the time. It allows new evidence to be submitted as things become clearer, so that funding reflects what is actually needed. The cost change process is now the formal way to make these requests.

We have made two submissions in 2026, both reflecting updated evidence and confirmed requirements. One covers strategic resource development, the other regulatory obligations. Since the Final Determination, further work has been done to refine scope, costs and delivery on both.

The first submission covers strategic water resource options, including the White Horse Reservoir and Teddington Direct River Abstraction. Both schemes are critical to long-term drought resilience and as development has progressed, additional spending is needed to keep delivery on track. In line with the PR24 framework, we are seeking access to part of the contingent allowance from the Final Determination to cover costs that could not be confirmed at the time.

The second submission covers investment needed to meet the Security and Emergency Measures Direction. The Drinking Water Inspectorate has required security enhancements across our operational sites, and while the need for this investment was recognised at PR24, further work was requested to confirm the best approach. That work is now complete. This submission sets out the updated investment required to deliver these essential regulatory improvements

Deferring our referral to the CMA

We have agreed with Ofwat, our regulator, that Ofwat will defer our appeal of their Final Determination to the Competition & Markets Authority (CMA) for 18 weeks from 18 March.

Over the last few weeks, following conversations with Ofwat, we are hopeful of unlocking a market led solution for the recapitalisation of Thames Water, including through an equity raise, without the need for a referral to the CMA.

This deferral is not a withdrawal of the request for the reference and Thames Water remains of the view that the Final Determination does not serve the interests of our customers, communities and the environment.

The challenges of our Final Determination

We’ve engaged with Ofwat to seek to secure a Final Determination that reflects our current position and supports our turnaround. While there has been progress, after a thorough review, it is clear that there remain significant gaps between the Final Determination and what we need to deliver for customers and the environment.

In our referral to the CMA, we are seeking:

• A regulatory settlement that reflects the circumstances of Thames Water’s operating area
• Targets that are challenging but achievable
• An appropriate balance of risk and return

There will be no delay to the delivery of our plans for year one of AMP8 as a result of this referral. Customer bills for 2025-26 will be unaffected.

Full details of our statement of case will be provided to the CMA in due course, in line with the process timetable.

Draft determination response

View our response to the draft determination:

Previous updates

View previous updates to our business plans.