On 18 November 2021 we and the Environment Agency announced investigations into all water and wastewater companies in England and Wales. This was after several water companies explained that they might not be treating as much sewage at their wastewater treatment works as they should be, and that this could be resulting in sewage discharges into the environment at times when this should not be happening.
During the course of the investigation we have published a number of updates, with the latest update in March 2026. Below are the previous updates we published between November 2021 and February 2026.
February 2026
On 5 February 2026 Ofwat confirmed its assessment that Southern Water has completed the actions it committed to via the section 19 undertakings secured following our 2019 investigation of the company.
December 2025
On 16 December 2025, Ofwat published its decision to accept an £11m enforcement package following findings that Wessex Water breached its legal obligations in operating its wastewater treatment works and network.
November 2025
On 11 November 2025, Ofwat consulted on proposals to accept an £11m enforcement package following findings that Wessex Water breached its legal obligations in operating its wastewater treatment works and network.
September 2025
On 9 September 2025, Ofwat confirmed £86.8m enforcement packages following findings that Anglian Water and South West Water breached their legal obligations in operating their wastewater treatment works and networks.
July 2025
On 29 July 2025, Ofwat proposed a £62.8m enforcement package following its finding that Anglian Water has breached its legal obligations in operating its wastewater treatment works and network.
On 10 July 2025, Ofwat announced a proposed a £24m enforcement package following its findings that South West Water has failed to meet it legal obligations in managing its wastewater treatment works and network. These failures resulted in the company spilling wastewater to the environment when it should not have done.
June 2025
On 4 June 2025, Ofwat announced the conclusion to its investigation into Northumbrian Water securing an enforcement package of £15.7m to be paid by the wastewater company and their shareholders, not customers.
This package is greater than the penalty which would otherwise have been imposed on the company. It ensures, this money will remain in the water sector and be spent on making improvements to services for the benefit of Northumbrian Water customers and the local environment. If a penalty had been applied, the money would have been returned to the Consolidated Fund operated by HM Treasury.
May 2025
On 28 May 2025, Ofwat announced the final decision in its investigation looking into the wastewater operations of Thames Water. The company and its shareholders will pay a £104.5m penalty for breaches of rules relating to its wastewater operations. This is the largest penalty Ofwat has ever issued.
In addition to this, an enforcement order has been applied requiring Thames Water to rectify the identified breaches relating to its wastewater operations. As part of the investigation into how the company was managing its treatment works and wider wastewater network, Ofwat uncovered failings that have amounted to a significant breach of the company’s legal obligations, which has caused an unacceptable impact on the environment and customers.
March 2025
On 20 March 2025, we concluded our investigation into Yorkshire Water and announced our decision to accept enforceable undertakings from the company.
The undertakings will require Yorkshire Water to take action to address the failures that we have identified during our investigation and bring itself back into compliance with its legal and regulatory obligations. As redress for its failures, it will also invest £40 million into improving the quality of rivers in its area through work with the Great Yorkshire Rivers initiative to remove artificial barriers in rivers, and by accelerating improvements at storm overflows in environmentally sensitive areas. This new investment is greater than the level of penalty that we would otherwise have imposed and will be funded by the company and its shareholders, not customers.
We welcome the fact that Yorkshire Water has acknowledged what has gone wrong and the steps it is taking to put this right. We will monitor its performance against the undertakings to make sure that it takes the necessary action to bring itself back into compliance.
August 2024
On 6 August 2024, we proposed that three water companies would be fined a total of £168m for failing to manage their wastewater treatment works and networks, as part of the first batch of outcomes from our biggest ever investigation.
The penalties proposed for consultation would see Thames Water fined £104m, Yorkshire Water fined £47m and Northumbrian Water fined £17m.
The penalties relate to their management of wastewater treatment works and wider sewer networks including their operation of storm overflows.
In addition to the proposed financial penalties, we also consulted on proposed enforcement orders which will require each company to rectify the problems we have identified to ensure they comply with their legal and regulatory obligations.
July 2024
On 16 July 2024, we announced the opening of enforcement cases into four more water and wastewater companies and has served formal notices on Dŵr Cymru Welsh Water, Hafren Dyfrdwy, Severn Trent and United Utilities. The opening of these enforcement cases follows detailed analysis of information on companies’ environmental performance and data about how often these companies spill from storm overflows. This has heightened our concerns that these companies may not be fulfilling their obligations to protect the environment and minimise pollution.
Opening these four new cases means that we now have enforcement activities underway against all 11 water and wastewater companies in England and Wales in relation to the operation of their wastewater businesses.
December 2023
Within this overarching investigation, we currently have enforcement cases against six companies.
We have now reached the next stage in our enforcement cases into companies’ management of their sewage treatment works and wider networks. We have notified Northumbrian Water, Thames Water and Yorkshire Water of our provisional findings in light of the evidence we have to date.
The companies will now have the opportunity to respond to our provisional findings, and to provide us with any further relevant evidence for our consideration. If we find a company has breached an obligation that Ofwat is responsible for enforcing, we have a duty, subject to certain exceptions, to issue an enforcement order to require the company to take steps to secure its compliance, unless we are satisfied that one of the exceptions to that duty apply.
This is an important stage of our investigation. It will ensure that we have provided the companies with the opportunity to respond to the provisional findings and that any future decisions in the case take account of their representations and any further evidence they might provide. Accordingly, we will consider any representations the companies make in reaching our final proposed decisions. We will then publish our proposed decisions for public consultation. Subject to due process, we expect to be able to do this in the first quarter of 2024. We will take public consultation responses into account as part of our final decisions on each of the cases.
As this investigation is ongoing, we cannot comment further on the detail of these cases for risk of prejudicing the investigation.
We are also continuing to progress the further three current wastewater enforcement cases opened as part of this overarching investigation; and are monitoring the remaining wastewater companies, that are not currently the subject of an enforcement case. As previously set out, the focus and scope of our enforcement cases may change as new information arises. We will continue to provide further updates as appropriate.
If Ofwat ultimately makes a finding of breach sufficient to warrant a fine, as part of its enforcement powers, Ofwat can impose a financial penalty on companies, the value of which can be up to 10% of relevant turnover. Where appropriate, Ofwat may decide not to issue an enforcement order, or decide to impose a reduced or no financial penalty at the conclusion of an investigation, where a company has come forward to formally commit to taking appropriate measures to secure its compliance and to provide suitable redress for its failures.
August 2023
We continue to progress the six enforcement cases we opened in 2022 to review how effectively water and wastewater companies operate their sewage treatment works. These cases are against Anglian Water, Northumbrian Water, South West Water, Thames Water, Wessex Water and Yorkshire Water.
We opened these cases after several water companies explained that they might not be treating as much sewage at their wastewater treatment works as they should be, and that this could be resulting in sewage discharges into the environment at times when this should not be happening. This is clearly a significant concern to us and customers.
Since opening our enforcement cases we have issued over 30 formal evidence requests to the companies concerned, and analysed over 3,000 pieces of quantitative and qualitative evidence that we have gathered. We are now moving to the next stages of our engagement with the companies currently subject to our enforcement cases.
For some this will be to gather further information from the company. For others, we are moving to complete our internal reporting process, following which we will confirm our analysis to date and our resulting findings with the company and provide the relevant companies with an opportunity to respond. We will then publish our findings and, where appropriate, our proposed action to remedy breaches that we have identified. This stage will provide opportunity for other interested stakeholders to comment before we conclude our final decisions.
This investigation is the largest Ofwat has ever undertaken. It is a priority for Ofwat and we are working as quickly as we can to progress it. As ever with investigations of this type, our timetable may change depending on what we uncover, whether we need to gather further information, and the next steps we decide to take to deliver the best outcomes for customers and the environment.
November 2022
One year ago, the Environment Agency and Ofwat launched separate major investigations into sewage treatment works. Ofwat Chief Executive David Black has written to customers on the progress of the Ofwat investigation.
June 2022
We continue to progress the five enforcement cases we opened in March 2022 (further detail below). In addition, we have opened a new enforcement case, into South West Water. This is due to our heightened concerns about its environmental performance across a number of metrics, that may suggest it is not complying with obligations Ofwat has powers to enforce. We have now issued South West Water with an information request under our formal enforcement powers to explore this further.
Beyond our enforcement cases, all water and wastewater companies in England and Wales remain subject to our on-going investigation into whether their wastewater treatment works are operating as they should. In July we will be writing to the remaining five companies to request updates on the progress of the plans they submitted to us in December setting out how they would address the issues they had identified at their treatment works and more generally improve their management of their environmental obligations.
What we’ve heard from water and sewerage companies so far.
For more information about our June 2022 update.
March 2022
On 18 November 2021, we wrote to all water and wastewater companies in England and Wales requesting that they provide a range of information to us about how they manage their wastewater treatment works, and in particular how they ensure they are meeting the flow to full treatment (FFT) requirements of their environmental permits. Where they are not, we asked companies to explain how they are putting that right and rebuilding trust with their customers on this issue.
All companies responded to us by the deadline of 22 December 2021. Their responses varied significantly in the level of detail they provided in answering our questions. This makes it difficult to draw sector-wide conclusions or comparisons between companies. Nevertheless, there are some useful headlines from what we have heard so far.
We have opened enforcement cases into five water companies (Anglian Water, Northumbrian Water, Thames Water, Wessex Water and Yorkshire Water). Concern about aspects of the information these companies submitted to us in December has prompted us to currently focus on them. However, all water and wastewater companies in England and Wales remain subject to our ongoing investigation as we continue to review the information we have gathered. We have now issued these five companies with formal notices to gather further information for enforcement purposes. This information will continue to help us further understand how these companies are managing compliance with their environmental obligations and inform our next steps.
For more information about our March 2022 update.
February 2022
We have now completed an initial assessment of the summary information we requested from wastewater companies, returned to us in December. It is helping us to start to build a picture of where companies may not be managing their wastewater treatment works in line with their environmental requirements, and the possible causes of that. The companies’ responses also set out where and how they are taking steps to put right any problems they have found and to rebuild their customers’ trust on this issue. The companies’ responses have varied in their level of detail and evidence, and in how well-advanced their plans are to put things right.
Whilst it is the Environment Agency and not Ofwat that is responsible for enforcing compliance with environmental permits, the responses indicate that there are issues here relevant to Ofwat’s regulatory role and powers. As set out below, this could include how water companies overall operate, manage and report on their performance, including of their wastewater treatment works. We will be asking more questions of companies.
Our analysis continues to the end of February, after which we will provide a further update on our next steps.
January 2022
We received responses to David’s Black’s letter, dated 18 November, from all wastewater companies by the 22 December. We are currently analysing those responses.
December 2021
Open letter from David Black, Interim Chief Executive to water customers: Our investigation into water companies
November 2021
Joint announcement from the Environment Agency, Ofwat and Defra: Press notice – Water companies could face legal action after investigation launched into sewage treatment works
Ofwat’s announcement of an investigation: