Ofwat investigates Dŵr Cymru sewage spills and network harm

UK Ofwat Publications & Enforcement

Filed March 12th, 2026

Detected March 13th, 2026

Summary

Ofwat has opened an enforcement investigation into Dŵr Cymru for alleged breaches related to sewage treatment works and network management, leading to environmental harm. The company has proposed undertakings valued at £44.72m, including a redress package, in lieu of a £40.6 million financial penalty.

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What changed

Ofwat has issued a proposed decision to accept undertakings from Dŵr Cymru in an enforcement case concerning the company's management of sewage treatment works and its sewerage network. The investigation identified breaches of the Urban Waste Water Treatment Regulations 1994 and the Water Industry Act 1991, stemming from inadequate asset management, monitoring, and reporting. Dŵr Cymru has proposed undertakings that include a £44.72 million redress package for customers and the environment, which Ofwat finds satisfactory to secure future compliance.

Regulated entities, particularly water and wastewater companies, should note the significant financial and environmental consequences of failing to adequately manage wastewater assets and comply with regulatory obligations. While Dŵr Cymru is proposing a redress package in lieu of a direct financial penalty, the scale of the proposed redress (£44.72m) and the potential penalty (£40.6m) highlight the financial risks. Companies must ensure robust systems for monitoring, maintenance, and reporting of wastewater operations to avoid similar enforcement actions and potential penalties.

What to do next

Review internal processes for wastewater asset management and monitoring.
Ensure compliance with Urban Waste Water Treatment Regulations and relevant industry acts.
Assess data gathering and analysis capabilities for operational performance reporting.

Penalties

Proposed financial penalty of £40.6 million (7.5% of relevant turnover), with a proposed redress package of £44.72m accepted in lieu.

Source document (simplified)

Enforcement case into Dŵr Cymru's management of its sewage treatment works and sewerage network

12 March 2026

Case summary

In July 2024 we opened an enforcement investigation into Dŵr Cymru to investigate whether it was managing its wastewater treatment works and networks appropriately, such that it limits spills and environmental harm from storm overflows.

This case is part of a wider investigation Ofwat has into all water and wastewater companies in England and Wales on this topic. For further detail about this investigation, how it has developed and the legal obligations being considered please see investigation into sewage treatment works.

In December 2025, we shared a confidential minded-to document with Dŵr Cymru as part of our informal ‘minded to’ process, outlined in our Statement of Policy on financial penalties.

Our minded-to document identified that Dŵr Cymru has breached:

Regulation 4(4), Regulation 4(2) and Schedule 2 of the Urban Waste Water Treatment (England and Wales) Regulations 1994 (UWWTR) by failing to operate and maintain its wastewater assets adequately, and to upgrade them where necessary, to provide sufficient performance. It has also failed to put in place adequate processes and systems to routinely monitor and maintain the capacity and performance of its assets to ensure they were meeting relevant legal requirements.
Section 94 Water Industry Act 1991 (WIA91) by systemically breaching its UWWTR duties and failing effectually to provide drainage and deal with the contents of its sewers.
Condition P12 of its licence, which requires it to have in place adequate resources and systems of planning and internal control to carry out its legal obligations, by failing to put in place adequate processes to identify and address emerging and present compliance risks effectively, to ensure that its data gathering and analysis were fit-for-purpose and to ensure that its Executive and Board received and/or sought sufficient information and assurance on the company’s operational performance. In response to our minded-to document, Dŵr Cymru put forward proposed undertakings under section 19 WIA91, setting out details of steps it will take to address the non-compliance we have identified to secure its future compliance. The undertakings also set out details of a proposed redress package valued at £44.72m. This will be funded by the company rather than customers.

Summary of Ofwat’s proposed decision

We were satisfied that the undertakings will secure the company’s compliance, and, subject to consultation, we are proposing to accept them. We have also concluded that it would be appropriate to accept the undertakings in lieu of the financial penalty we would otherwise impose in this case (£40.6 million, 7.5% of its relevant turnover). The £44.72 million redress package will deliver a better outcome for customers and the environment by means of:

£40.66 million to be targeted at reducing spills at specific overflows with additional investment planned at sites during the 2025-30 period with the dual aim of addressing harm and reducing annual spills to below 20 at the relevant overflows; and investigating and sealing works on private parts of the sewer network to tackle groundwater infiltration which is a significant contributor to frequently spilling overflows.
£2.0 million to fund the mitigation of barriers to fish movement and habitat improvement in Welsh rivers;
£1.0 million to fund the creation and resource a joint misconnections taskforce; and
£1.066 million as part of a community environment fund (Cymuned Natur) that Dŵr Cymru will establish to provide grants to third parties upon successful application for projects intended to preserve and/or enhance the local environment, water quality, bathing water quality or biodiversity within Dŵr Cymru’s operating area. The undertakings would be enforceable by us under section 18 WIA91 and we would monitor Dŵr Cymru’s delivery of them.