Data from environmental regulator Natural Resources Wales (NRW) shows Dŵr Cymru was responsible for a total of 155 pollution incidents during 2024
12:11, 21 Jul 2025Updated 12:32, 21 Jul 2025
Of the total number of incidents, Dwr Cymru was responsible for six serious (category one or two) incidents – a drop from seven last year.(Image: John Myers)
The number of pollution incidents caused by Dŵr Cymru went up again in 2024 – with the highest number of sewage pollution incidents in ten years recorded in 2024. Data shows there were 155 pollution incidents, up from 132 the year before. Every year, bar two, of the last decade, the number of incidents has risen.
Data from environmental regulator Natural Resources Wales (NRW) shows Dŵr Cymru was responsible for a total of 155 pollution incidents during 2024 – 132 from sewerage assets and 23 relating to water supply.
While water supply incidents have dropped in recent years, sewage incidents are continuing to rise, increasing from 89 in 2022 to 132 in 2024, a 42% increase in the last ten years.
Of the total number of incidents, the company was responsible for six serious (category one or two) incidents – a drop from seven last year.
The latest pollution incident report says: “Over the past decade, the number of pollution incidents caused by Dŵr Cymru in England and Wales has generally increased.
“In 2024, the company experienced the highest number of sewage pollution incidents since 2015, as well as the second-highest overall total of pollution incidents during this period.”
There were six pollution incidents listed as “serious” by the regulator in 2024, down one on the year before, but double the 2021 figure.
The report also lists the number of pollution incidents caused solely by Dŵr Cymru’s sewerage assets. Between 2015 and 2020, pollution incidents per unit of sewer length decreased, but have risen each year over the past four years, reaching a ten-year high of 36 incidents per 10,000 km of sewer in 2024.
The top source of pollution from assets owned by Dŵr Cymru over the last decade was foul sewers, far in excess of the other things in the top five – combined sewer overflows, water treatment works, pumping stations, and the water distribution system.
While incidents from foul sewers and treatment works have generally declined, pollution from combined sewer overflows, pumping stations and the water distribution system are rising.
The report also looks at the performance of Hafren Dyfrdwy, which also operates in Wales. Over the past decade, pollution incidents from Hafren Dyfrdwy’s sewerage and water assets have generally declined, with a brief rise in 2020–21 before falling again in the last three years.
Pollution incidents caused solely by Hafren Dyfrdwy’s sewerage assets doubled in 2024 from 20 in 2023.
Pollution incidents come from various assets, with the top causes over the last 10 years being the water distribution system, combined sewer overflows and foul sewers.
NRW says it can take action from giving advice right through to prosecution in the courts but it does warn in the report that complex investigations can take years.
Since 2015, the regulator says it has issued four notices, 24 formal cautions and ten prosecutions.
Dŵr Cymru has been ordered to pay £1.9m in prosecution fines. It has also agreed to enforcement undertakings, which has resulted in a £174,500 contribution from Dŵr Cymru to local environmental charities and projects since 2015.
Also published was the storm overflow report. There are over 2,000 permitted storm overflows across Wales. These systems are designed to relieve pressure on the sewer network during heavy rainfall, when sewers can become overwhelmed. Each overflow needs a permit from NRW to be allowed to legally discharge.
Dŵr Cymru has 2,064 storm overflows. Almost all of Wales’ storm overflows have monitoring equipment and the average number of spills per storm overflow fell in 2024 to 48.9 from 55.3 the year before.
In 2024, the spill duration rose from 7.1 hours in 2022 to 8.2 hours in 2024.
For Hafren Dyfrdwy, all the overflows have monitors. Average spills per overflow increased from 29.0 in 2022 to 38.8 in 2023, before falling slightly to 36.2 in 2024.
NRW says it successfully prosecuted Dŵr Cymru Welsh Water over incidents on the Gwent Levels and a tributary of the Afon Llwyd.
It says it has introduced new guidance and secured record levels of investment.
In the coming year, the regulator says it will introduce a new team to increase monitoring of water company discharges, compliance checks and audits as well as new guidance about reduction plans.
Head of regulation and permitting from NRW, Nadia De Longhi, said: “We’ve seen a huge deterioration in the performance of Dŵr Cymru Welsh Water since 2020, and despite repeated warnings and interventions they’ve been unable to reverse this concerning trend.
“This has left us with no choice but to pursue a number of prosecutions against the company which have recently concluded. This is not the outcome we want, nor the best outcome for the environment – our priority will always be to bring companies into compliance and prevent environmental damage from happening in the first place.
“We continue to do everything we can to drive improvements, but Dŵr Cymru Welsh Water must address the root cause of these pollution incidents and take preventative measures before more harm is done to the water environment.
A Dŵr Cymru Welsh Water spokesperson said: “We acknowledge the concerns raised in the report and accept that while the number of serious pollution incidents has slightly reduced, our performance is not where it needs to be. The industry across the UK has seen increases in pollution incidents.
“We are rightly being held to a higher standard and have improved our processes to meet this challenge, with better monitoring leading to detecting more short-lived event and better reporting.
“We are accelerating investment in key areas to reduce pollution incidents with a £4bn investment programme that includes £2.5bn on environmental projects.
“While we have made progress, such as increasing the number of incidents we find and self-reporting, we know more needs to be done.
“We remain committed to working constructively with NRW to deliver improvements and will be engaging closely on their new requirements and guidance, including the development of pollution incident reduction plans and further use of smart technology to spot problems in the sewer network before they can cause a pollution.”
A spokesperson for Hafren Dyfrdwy said: “We are pleased to remain a strong performer after seeing a steady decrease in pollution incidents and no serious pollutions since we began in 2018.
“We are encouraged by the real progress we have made in reducing spills from our storm overflows. However, we recognise the many challenges facing our environment today and, in the future, and remain committed to further driving down pollution incidents and spill numbers. We are delivering an ambitious environmental plan that will help to deliver a range of solutions to help reduce spills and our first Pollution Incident Reduction Plan will be published early in 2026.”
NRW’s full annual environmental performance report for both water companies, with the updated star rating for Dŵr Cymru Welsh Water, will be published this autumn.