- Drinking Water 2025 – Summary of the Chief Inspector’s report for drinking water in England
- Foreword
- Water supplies and testing
- Compliance with water quality standards
- Learning from microbiological failures
- Learning from turbidity failures
- Learning from chemical, taste and odour failures
- Learning from pesticide failures
- Asset health and service reservoir integrity
- Consumer contacts
- Drinking water quality events
- Water safety planning and risk assessment
- Perfluoroalkyl and polyfluoroalkyl substances (PFAS)
- Audit programme completed by the Inspectorate
- Air valve audits
- Enforcement, transformation and recommendations
- Materials in contact with drinking water (regulation 31)
- Security and Emergency Measures Direction - SEMD
- Network and Information Systems - NIS
- Research publications
- Whistleblowers
- Working with stakeholders
- Annex A – Number of tests carried out by companies
- Annex B – Compliance with standards
- Annex C – Compliance failures and events
Asset health and service reservoir integrity
Asset health remains central to the protection of drinking water quality. During 2025, there were 49 coliform compliance failures at treatment works and 65 at service reservoirs. There were also three E. coli detections at treatment works and four at service reservoirs from a total of 3,632,669 microbiological tests. Ingress into contact tanks, treated water tanks and service reservoirs remains a recurrent risk, demonstrating the importance of maintaining the integrity of treated water storage and post-treatment assets.
In addition to these compliance failures, 47 water quality events were attributed directly to poor asset health or plant failure. These included 30 microbiological contamination events and 17 structural failures affecting treatment works, treated water tanks or service reservoirs. A further 24 events were associated with treatment works plant failure. These figures demonstrate that asset condition, inspection quality and timely remediation remain critical to preventing events and protecting consumers.
Companies are expected to understand and maintain their assets through risk-based inspection and maintenance programmes. Physical internal inspections remain important because they provide greater assurance than remotely operated vehicle inspections alone and allow walls, roofs, floors and internal structures to be cleaned and assessed in detail. While the Principles of Water Supply Hygiene identify ten years as the maximum advised interval for treated water storage inspections, the Inspectorate expects companies to adopt shorter, risk-based frequencies where asset age, condition, previous defects, microbiological history or operational importance indicate a higher risk.
Over the past six years, the Inspectorate has increased scrutiny of service reservoirs and tanks through the service reservoir and tanks data return. This has improved visibility of inspection frequency, inspection quality and the robustness of remedial works. The 2025 dataset identified 195 tanks that had not been inspected within the maximum advised interval, representing 3.1% of tanks. This is unchanged from 2024 but remains an improvement compared with 4.9% in 2023 and 6.0% in 2022. Although this indicates progress, overdue inspections continue to present a residual risk that companies must manage and reduce.
| Company | Number of tanks within maximum inspection frequency | Number of tanks overdue | Overdue (%) |
|---|---|---|---|
| ANH | 732 | 52 | 6.63% |
| BRL | 181 | 0 | – |
| CAM | 37 | 0 | – |
| NES | 518 | 7 | 1.33% |
| PRT | 34 | 3 | 8.11% |
| SES | 68 | 4 | 5.56% |
| SEW | 310 | 35 | 10.14% |
| SRN | 330 | 5 | 1.49% |
| SVT | 797 | 37 | 4.44% |
| SWB | 483 | 16 | 3.21% |
| TMS | 644 | 18 | 2.72% |
| UUT | 639 | 5 | 0.78% |
| WSX | 560 | 5 | 0.88% |
| Total | 5333 | 187 | 3.39% |
For this analysis, reservoirs identified as abandoned or out of service were manually removed from the dataset. From 2026, the Information Direction will include a specific field to capture asset status more consistently. This will improve the quality of the dataset, reduce the need for manual adjustment and support more reliable scrutiny of inspection performance.
Portsmouth Water made notable progress during 2025, reducing the proportion of reservoirs overdue for inspection from 16% to 8.82%. Although this remains the second highest rate in the industry, the improvement demonstrates that focused action can reduce overdue inspections and improve assurance over treated water storage assets. The Inspectorate expects companies with overdue inspections to maintain clear, risk-based programmes for completing inspections and any associated remedial works.
Figure 7 – Reservoir inspection data
Figure 8 – assets not inspected within past 10 years
Events relevant to asset health in 2025
Anglian Water – Stonewall reservoir 2A
Stonewall Reservoir 2A was last internally inspected in October 2017. Following repeat coliform detections, the company undertook a further inspection approximately eight years later, which identified 18 separate roof ingress points. The findings confirmed that the integrity of the treated water storage asset had been compromised and that there was a credible pathway for contamination.
The Inspectorate had taken enforcement action in early 2023 requiring Anglian Water to complete internal inspections of all treated water tanks that had not been inspected within 10 years, with agreed milestones to mitigate microbiological risk. The notice was revised on 24 February 2023 to strengthen procedural requirements. The Inspectorate concluded that the company had not established and implemented an appropriate risk-based inspection frequency, as required by the notice.
Despite a final completion deadline of 30 April 2025, the company later advised that it would be unable to inspect 23 tanks within this period. Separate regulation 28(4) notices were therefore issued with extended deadlines, many of which were subsequently delayed further. The Inspectorate considered these delays to constitute a failure to comply with regulation 28(4) and section 68(1) of the Water Industry Act 1991, raising significant concerns about asset resilience and protection of drinking water quality. As the contravention was not trivial, further enforcement is ongoing and will be reported in the 2026 report.