Records of Storm Overflow Removal by Dŵr Cymru Welsh Water in Cynon Valley Key Findings
- Comprehensive Removal Not Evidenced
There is no public record or evidence confirming the complete removal of storm overflows (also known as Combined Storm Overflows, CSOs) into rivers or watercourses by Dŵr Cymru Welsh Water or its contractors in the Cynon Valley. Industry statements and official documentation indicate that total removal of storm overflows from the system is regarded as unaffordable and impractical, potentially taking decades if attempted at all. This is due to the nature of legacy sewerage infrastructure and the scale of the intervention that would be required. - Focus on Improvement, Not Elimination
Dŵr Cymru Welsh Water’s strategy prioritizes reducing the impact of spills, upgrading existing assets, and meeting stricter environmental standards. Their investment programs (2020–2025, and planned for 2025–2030 and beyond) aim to target and improve storm overflows causing the highest environmental impact rather than remove them. Upgrades include enhanced monitoring and storage to ensure discharges are controlled and their frequency reduced, particularly for overflows rated as ‘unsatisfactory’ by regulators. - Cynon Valley Specifics
No published Welsh Water report or local authority flood investigation explicitly lists or documents the removal of storm overflows in the Cynon Valley. Most records, including those from Rhondda Cynon Taf County Borough Council, relate to maintenance, clearing, and upgrades (such as inlet improvements, blockage removal, or temporary control measures during events like Storm Dennis) rather than the physical disconnection or elimination of storm overflows from watercourses. Where issues have arisen, actions have generally centered on maintenance or upgrades to culvert inlets and monitoring equipment. - Regulatory and Planning Approach
The prevailing approach—supported by Natural Resources Wales and taskforces such as the Wales Better River Quality Taskforce—is to investigate, classify, and reduce environmental harm from storm overflows. There is a robust program of monitoring and planned investment for improvements, but not full removal, especially within mixed urban and river valley settings like the Cynon Valley.
There is no single, definitive public record specifying the exact number of Combined Storm Overflows (CSOs) in Cynon Valley. However, official data from Dŵr Cymru Welsh Water and public environmental sources provide further context:
Summary Table: Activities Documented for Storm Overflows
- Dŵr Cymru Welsh Water’s Storm Overflow Reporting: Dŵr Cymru’s 2022 annual return, as submitted to regulators, lists all storm overflows in Wales with associated locations and reference numbers. However, these datasets are not explicitly organized by local areas such as “Cynon Valley” for direct counting, instead listing each outfall by asset name/reference and National Grid location. To determine the precise number for Cynon Valley, one would need to cross-reference all local asset names and locations within the Cynon Valley catchment.
- Regional Context: Across Wales, there were 1,946 storm overflows listed in Welsh Water’s annual return for 2022 (excluding those owned by Hafren Dyfrdwy). Each river valley, especially urbanized catchments like the Cynon, typically contains multiple CSOs along principal watercourses and tributaries, including at or near wastewater treatment works, major junctions, and older combined sewer sections.
- Tools for Identification: Dŵr Cymru Welsh Water recently published an interactive storm overflow map with real-time and asset data, allowing users to view locations and details of storm overflows across their network. This map is the most practical way to accurately determine up-to-date numbers and locations of CSOs in the Cynon Valley at any given time.
- Local Observations: Environmental groups and local news routinely report on the presence and impact of CSOs in the Cynon Valley, confirming their existence at sites discharging into the River Cynon and its urban tributaries. Exact counts in these reports are not provided.
In summary:
A precise, up-to-date figure for the number of Combined Storm Overflows within just the Cynon Valley is not directly available in published annual datasets or reports. The best approach is to consult the new real-time Welsh Water overflow map, as it aggregates the latest permitted and monitored storm overflow locations and would enable a user to count those specifically within the Cynon Valley area
NRW steps up regulatory action as water company fails to curb sewage pollution incidents
Dŵr Cymru Welsh Water must make urgent and fundamental changes to its operations, according to regulator Natural Resources Wales (NRW), as the company records the highest number of sewage pollution incidents in ten years.
New data released today shows that the company 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, 107 in 2023 and 132 in 2024. This represents 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. Five of these were from sewerage assets and were all category two.
Analysis over the last ten years shows that the main source of incidents come from foul sewers (423), storm overflows (168) and water treatment works (166).
NRW has taken the following actions to improve water company performance:
- Secured successful prosecutions for offences relating to Dŵr Cymru Welsh Water’s self-monitoring responsibilities and pollution incidents on the Gwent Levels and a tributary of the Afon Llwyd.
- Secured record levels of water company investment in the environment between 2025-2030 through the Ofwat price review process.
- Required water companies to prioritise action for assets known to cause the most harm to the environment.
- Introduced new guidance about the conditions under which a storm overflow is permitted to spill, and when a spill is in breach of its environmental permit.
In 2025 NRW will:
- Introduce a new team to increase monitoring of water company discharges, compliance checks and audits.
- Introduce guidance linked to new legislation for Pollution Incident Reduction Plans, which set new targets to challenge water companies to deliver annual improvements.
- In conjunction with the Environment Agency in England, tighten the framework for annual performance assessments to come into force from 1st January 2026.
Nadia De Longhi, Head of Regulation and Permitting from NRW, 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.
“We will be increasing our capacity for monitoring and auditing discharges, clamping down on unpermitted storm overflows and introducing tighter criteria for annual performance reporting. This will ensure we are receiving the best quality data about the impact of water company operations on the environment and can respond appropriately.”
Hafren Dyfrdwy, which provides drinking water and wastewater services to some of the mid and north Wales border counties, was responsible for five pollution incidents – two of which were from sewerage assets. This also represents an increase from one sewage pollution incident in 2023 and four in total. The company has not been responsible for any serious incidents since it was formed in 2018.
The number of incidents self-reported by Hafren Dyfrdwy dropped last year, falling to 60%, while Dŵr Cymru Welsh Water increased their self reporting of incidents from 70% in 2023 to 74% in 2024. Both still fall short of the 80% target set by NRW.
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.
Today’s pollution incident report has been published to provide an interim update on pollution incidents and a focussed look at the data over a ten year period.
Also published today is NRW’s annual spill data report, with analysis on 2024 data for storm overflow spills.
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