Natural Resources Wales (NRW) has published its 2025 annual environmental performance reports and storm overflow spill data for Dŵr Cymru Welsh Water and Hafren Dyfrdwy.
The results show progress alongside ongoing challenges. Hafren Dyfrdwy continues to perform strongly in several areas, while Dŵr Cymru Welsh Water has shown improvements in some measures but remains a company requiring improvement in line with the Environmental Performance Assessment (EPA).
Although Dŵr Cymru Welsh Water’s pollution incidents from wastewater assets fell from 132 in 2024 to 107 in 2025, serious pollution incidents increased from 6 to 9 in the same period.
The number of serious pollution incidents is the highest recorded under the current assessment framework and a significant cause for concern. Every serious incident, by definition, causes environmental damage. The continued occurrence of these incidents highlights the need for action to reduce the harm they cause.
The company improved storm overflow monitoring, reduced some pollution indicators and increased self-reporting of incidents. However, reporting rates remain below expectations and concerns remain around permit compliance, wastewater treatment compliance and the pace of environmental improvement.
Dŵr Cymru Welsh Water is Wales’ largest provider of drinking water and wastewater services, while Hafren Dyfrdwy, part of the Severn Trent group, provides services to parts of north and mid Wales.
Hafren Dyfrdwy does not receive an EPA star rating because of its smaller size, but NRW still publishes an assessment of its environmental performance.
In 2025, the company performed well in several key areas, with no serious pollution incidents and an excellent level of compliance with wastewater discharge permits for the third year in a row.
It also recorded just 3 incidents overall, down from 5 in 2024 and the lowest number since 2015. One incident was not self-reported.
Storm overflow spill data for 2025 shows both water companies recorded fewer spills than in the previous year, alongside improved reliability of monitoring equipment. However, frequent spilling remains a significant concern. Across Wales, almost a third of monitored overflows spilled between 40 and 99 times during 2025, while more than one in 10 spilled over 100 times.
Nadia De Longhi, NRW’s Head of Regulation said:
“These results show some encouraging signs of progress, but the overall picture remains mixed.
“Hafren Dyfrdwy continues to perform strongly, with year-on-year improvements in several areas. It is also positive to see improvements in some aspects of Dŵr Cymru Welsh Water’s performance, including fewer pollution incidents and better storm overflow monitoring.
“However, serious pollution incidents remain a significant concern. Every serious pollution incident causes environmental harm, and reducing these incidents must remain a priority.
“Stronger regulation, increased monitoring and significant investment are helping to drive improvements, but it will take time for these changes to deliver the level of environmental improvement that people rightly expect to see across Wales.”
The full reports are available on the NRW website:
Annual performance report for Dwr Cymru Welsh Water
Annual performance reports for Hafren Dyfrdwy
Storm overflow spill data reports.
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