- Drinking Water 2025 – Summary of the Chief Inspector’s report for drinking water in Wales
- Foreword
- Introduction
- Water supplies and testing
- Compliance with standards
- Learning from compliance failures
- Learning from events
- Consumer contacts
- Asset health
- Water safety planning and risk assessment
- Poly and perfluoroalkyl substances (PFAS)
- Audit programme
- Recommendations
- Enforcement
- Security and Emergency Measures Direction - SEMD
- Network and Information Systems - NIS
- Materials in contact with drinking water (Regulation 31)
- Research publications
- Whistleblowers
- Working with stakeholders
Audit programme
| Company | Audit name |
|---|---|
| DWR | Bolton Hill WTW – raw water deterioration and process breakthrough |
| DWR | Retailers desktop |
| DWR | Retailers desktop – Welsh Water supplied – note separate to DWR itself |
| HDC | Retailers desktop |
| DWR | Bottled water stores |
| DWR | Llyswen WTW and Llanigon SRV |
| DWR | Disinfection Policy desktop |
During 2025, the Drinking Water Inspectorate carried out a programme of targeted audits to provide assurance that drinking water supplied to consumers in Wales remained safe, reliable and well managed. These audits form part of the Inspectorate’s routine regulatory work and are designed to test how effectively water companies manage risks to drinking water quality, particularly where past incidents or emerging concerns have highlighted potential weaknesses.
The audits undertaken in 2025 provided a detailed and practical assessment of how drinking water quality is managed across treatment works, distribution systems, emergency arrangements and non-household supply chains. They identified evidence of good operational practice, including effective treatment performance, improved outcomes from targeted capital investment and a strong baseline understanding of regulatory responsibilities. However, the audits also highlighted recurring weaknesses that could affect resilience, particularly in relation to clarity of documentation, consistency of risk assessment, assurance of critical control measures, and the management of assets, hygiene and operational procedures under both routine and challenging conditions.
Taken together, these findings demonstrate that while systems are generally effective under normal operating conditions, further work is required to strengthen robustness, transparency and preparedness. The suggestions and recommendations made to companies in assessment letters focused on areas such as end-to-end testing of critical controls, formalisation of procedures and decision-making frameworks, enhanced monitoring and data use, and better coordination and training for incident response. By addressing these areas and embedding learning from both audits and operational events, companies can build greater resilience, maintain compliance under a wider range of conditions, and continue to protect public health and consumer confidence.
DWR Bolton Hill works
The Drinking Water Inspectorate’s technical audit of Bolton Hill works identified generally sound operational practices, with orderly record keeping, well-maintained control systems and core treatment processes, including coagulation, dissolved air flotation clarification, rapid gravity filtration and granular activated carbon adsorption, operating broadly effectively. The site uses an automated coagulant dose optimisation system linked to live UV254 data, supported by jar testing validation, while triple-validated pH monitoring provides resilience in chemical dosing control. Routine monitoring and escalation arrangements for raw water quality at both intake stations and site inlet were also identified as positive features supporting operational awareness.
However, the audit highlighted important weaknesses in critical control assurance that could undermine resilience to raw water deterioration and breakthrough events. Notably, end‑to‑end functional testing of alarms and shutdown systems was not routinely undertaken, with real-world events being relied upon as evidence of performance. This creates a risk that monitor or communication failures could go undetected. Similarly, limited SCADA visibility of individual instrument performance, such as only displaying averaged values in triple‑validated systems without deviation alarms, reduces operators’ ability to identify faults affecting key control points.
Several operational and asset-specific issues were also observed on site. For instance, saturated oil absorbent mats were found beneath a flocculator drive, highlighting the need for clearer spill response and food-grade oil assurance, while rapid gravity filter operation presented potential risks due to fast return‑to‑service rates and temporary turbidity alarm suppression, increasing the likelihood of undetected breakthrough. In addition, historic GAC management practices were shown to have resulted in low iodine numbers across multiple contactors in spent media, indicating reduced adsorptive capacity and the need for accelerated regeneration strategies. The company have since instituted a minimum iodine number target to provide additional assurance of ongoing GAC performance across their assets.
Shortcomings in sampling, hygiene, and asset condition were also identified. Operational sample taps were found in poor hygienic condition and lacked clear flushing instructions, while site observations included mole activity on treated water storage embankments (Figure 40), raising ingress risks. Other issues included potential backflow risks in GAC washwater systems due to the absence of an air gap, and reliance on operator judgement for key decisions such as pump recommissioning and raw water response actions, often without defined decision trees or standardised procedures.
Overall, although only one formal recommendation was made, requiring a risk-based programme of end-to-end functional testing of critical alarms, the audit identified multiple areas where operational discipline, process verification and risk management need to be strengthened. The findings indicate that, although the works is generally well operated, improved assurance of critical controls, clearer procedures and more robust monitoring and sampling arrangements are essential to ensure resilience against challenging raw water conditions and to maintain consistent compliance.
DWR bottled water storage and management
One of the audits undertaken in 2025 examined the management of bottled water stores at two sites, Dinas and Kinmel Park. Bottled water is a critical part of emergency arrangements, particularly during loss of supply events, and must be stored and managed in a way that protects its quality from the point it is received by the company to the point it is delivered to consumers.
The audit took place in July 2025 and was prompted by the Inspectorate’s planned audit programme, as well as by recent industry events that had highlighted weaknesses in alternative supply arrangements; all companies across the industry were audited. In particular, a significant loss of supply event earlier in the year had demonstrated the pressures placed on bottled water storage and distribution systems during emergencies. The audit therefore focused on how well these systems function under both normal and event conditions.
Inspectors found that some aspects of bottled water management were positive. Procedures for accepting and storing bottled water were broadly aligned with industry guidance, and there was evidence that the company was reviewing its arrangements in response to recent events. However, the audit also identified a number of areas where improvements were needed.
At the Dinas site, bottled water was found in a building that was officially out of service due to structural issues. Despite signage indicating that parts of the building were not in use, some bottled water stored there was later distributed for consumption. The Inspectorate considered this inappropriate, given the risk of contamination from damaged walls and the potential presence of vermin. The company was advised that any storage facility identified as posing a risk to water quality should be taken fully out of service until made safe and secure.
The audit also highlighted weaknesses in stock management and tracking. Inspectors found that batch numbers were not always recorded correctly and that information was sometimes shared informally, increasing the risk of errors. This made it difficult to trace bottled water once it had been moved between sites and would limit the company’s ability to respond effectively if a batch needed to be recalled. While plans were in place to introduce a more robust tracking system, the Inspectorate required updates on its implementation and stressed the importance of accurate records.
Further concerns were raised about how bottled water quality was assured on receipt from suppliers. Bottled water was not always sampled at the point it entered the company’s control, and certificates confirming compliance at the time of bottling were not routinely obtained. Although the company took steps to update its procedures following the audit, the Inspectorate emphasised that assurance should be in place before water is made available for distribution to consumers.
Overall, the audit concluded that while bottled water is an essential safeguard during emergencies, it should be treated with the same level of care and scrutiny as other parts of the drinking water supply system. The Inspectorate made several recommendations and required the company to demonstrate how it would strengthen storage conditions, tracking arrangements and risk assessment processes to ensure bottled water remains safe at all times.
DWR disinfection policy
Disinfection is a fundamental barrier against harmful organisms in drinking water, and the policy sets out how treatment processes are designed, monitored and validated to protect public health. This audit was carried out as a desktop exercise during October and November 2025 and followed an earlier audit in which drinking water safety planning had been reviewed.
The purpose of the audit was to assess updates made to the disinfection policy and to determine whether it provided clear, reliable and evidence-based guidance for operational staff. Inspectors reviewed a range of documents covering treatment processes, performance targets and site-specific assessments.
The audit found that, while the policy addressed many relevant issues, there were significant areas where clarity and consistency were lacking. In several cases, the Inspectorate could not determine how key figures or targets had been derived, or whether they were supported by appropriate reference material. This included how treatment performance targets were set and how data was selected and analysed to demonstrate compliance.
Inspectors also identified concerns about how monitoring data was used. In some cases, data was assessed over rolling periods without clear definitions, which could allow poor performance to be obscured when older results dropped out of the assessment window. The Inspectorate considered this approach to pose a risk, as it could delay the identification of emerging problems and weaken the overall level of protection.
Another important issue related to how exceedances or failures would be managed. The policy did not always explain what actions should be taken if treatment performance fell below the required standard, or when such situations should be reported to the Inspectorate. Clear escalation and response arrangements are essential to ensure that risks are managed promptly and transparently.
The audit concluded that, although the company had invested effort in developing its disinfection policy, further work was required to ensure that it was fully robust, transparent and aligned with current scientific guidance. The Inspectorate made several recommendations and required the company to provide detailed responses and evidence to demonstrate how the policy would be strengthened.
DWR and HDC retailers
In Wales, the retail market differs from that in England, with non-household customers eligible to switch retail provider where their usage is greater than 50 million litres per annum. Although this reduces the number of properties in the customer base, these properties may present higher risk to the wider network because they are more likely to have complex plumbing systems or secondary private supplies. In Wales, two wholesalers and six retailers are involved in the supply of water to consumers. Across audits of non-household water quality and sufficiency management, findings indicated generally sound high-level arrangements and a good understanding of regulatory responsibilities among wholesalers and retailers.
However, several systemic gaps were identified that could affect resilience during water quality or supply incidents, including unclear and inconsistently documented roles and responsibilities, limited formalisation of communication arrangements, and insufficient recording and sharing of customer contacts and water quality intelligence. A key theme across the retailer audits was limited experience of water quality events and incidents, including escalation of urgent issues. This appeared to reflect limited opportunity, as relatively few occurrences have affected these consumers.
The absence of joint scenario-based emergency planning and training exercises was also noted, creating potential risks to preparedness and coordination during incidents. The audits also identified suggested improvements to staff training, particularly for frontline call handling, and limited mechanisms to track or escalate non-household customer issues.
Overall, while current arrangements appear adequate under normal conditions, the Inspectorate concluded that greater procedural clarity, proactive collaboration, and strengthened preparedness are needed to ensure robust protection of water quality and supply for non-household consumers.
DWR Llyswen works and Llanigon service reservoir completed capital scheme
The Drinking Water Inspectorate’s audit of Llyswen works and Llanigon service reservoir found that recent capital investment, including large-scale replacement of deteriorated iron mains, targeted network cleansing, and treatment process upgrades, has begun to deliver measurable improvements in water quality. These interventions have reduced the mobilisation of historic sediment, improved chlorine stability across the network, and contributed to a decline in discolouration contacts, supported by increases in residual chlorine observed at downstream booster locations and improved flow stability following installation of variable speed pumping.
Operational control and system resilience were generally assessed as effective, with good practice evident in areas such as pressure monitoring (figure 43) with clearly defined operating ranges, adaptive flow control to reduce surge impacts, and the management of supply during complex commissioning activities. Coagulation, clarification, and filtration processes were performing well under variable raw water conditions, demonstrating effective optimisation following earlier site upgrades.
However, the audit identified several areas requiring further strengthening. Hygiene risks were observed in the storage and handling of temporary pumping equipment and pipework, while chemical management issues included insecure or damaged packaging and unclear containment arrangements for bulk deliveries, indicating potential contamination pathways (figure 44). Asset security and integrity also require improvement, with examples including non‑secure hatches, inadequate sealing arrangements, and insufficient perimeter protection, alongside risks associated with ancillary infrastructure such as unprotected air valves and nearby land use activities that could introduce contaminants.
The new valve complex (figure 45), including air valves, at Llanigon service reservoir had been located on a throughway, used to move livestock between fields. This was also downhill from two large muck heaps, leading to risk of run off into the chambers. The Inspectors identified that damage to the concrete surround had already occurred, further increasing the risk. In response the company initiated regular inspections and recommendations were made to take steps to mitigate the risk, including removal of the muck heap, repairs to the concrete and covers and the frequency of inspection was reviewed for air valves at service reservoirs.
The Inspectorate also highlighted the need for greater clarity and robustness in operational and investigative practices. Discolouration root cause analysis lacked sufficient evidential basis in some cases, with limited consideration of contributing parameters such as iron, manganese, and aluminium. Sampling arrangements and monitoring definitions were at times unclear, particularly during transitions in asset configuration, and there were gaps in demonstrating disinfection performance and contact time control during operational changes. These issues were compounded by a reliance on operational judgement in the absence of clearly defined procedures and consistent data interpretation.
Overall, the findings indicate clear progress following significant investment, but emphasise that sustained operational discipline, improved procedural clarity, and stronger asset and risk management controls are essential to secure and maintain these gains and to ensure consistent long‑term compliance.
Conclusion
The audits undertaken in 2025 provided valuable insight into how drinking water quality is protected across emergency arrangements and routine treatment processes. They highlighted good practice, but also showed that continued attention is needed to ensure systems, policies and documentation remain clear, consistent and effective. By addressing the recommendations made, water companies can strengthen public confidence and ensure that the safety of drinking water remains the highest priority.