- 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
Asset health
Treated water tanks and service reservoirs
During 2025, there were three coliform compliance failures at water treatment works and 18 at service reservoirs. There were no E. coli detections at treatment works and two at service reservoirs. Ingress into contact tanks and service reservoirs remains a recurrent issue and represents a residual risk, as these results demonstrate.
Companies are expected to understand and maintain their assets through a programme of physical inspections, which may be supplemented by inspections using remotely operated vehicles. The Inspectorate considers physical inspections necessary because they provide clarity and better resolution than remotely operated vehicle inspections and enable cleaning of walls and structures within the reservoir during the same isolation and drain-down activity. Although 10 years is the maximum interval advised in the Principles of Water Supply Hygiene for treated water storage, the Inspectorate recommends that inspections are carried out more frequently on a risk-based basis.
The Inspectorate has increased scrutiny of service reservoirs and tanks, including through the service reservoir and tanks data return, to assess the quality of inspections and the robustness of remedial works. Analysis of the most recent dataset highlights continued weaknesses in inspection frequency, with 195 tanks out of 6,312 nationally not having been inspected for more than 10 years. In Wales, the combined figure is eight out of 815 reservoirs. This represents a significant overall improvement compared with the initial data return in 2021, which showed 457 tanks overdue or with no inspection record across the industry, including 50 in Wales. However, reservoirs continue to represent an area of risk requiring attention.
| Company code | Number of tanks inspected within 10 years | Number of tanks in supply overdue inspection (>10 years) | Total number of tanks | Percentage of tanks overdue inspection (>10 years) |
|---|---|---|---|---|
| HDC | 112 | 7 | 119 | 5.88% |
| DWR | 692 | 1 | 693 | 0.14% |
| Wales total | 807 | 8 | 815 | 0.98% |
Figures 37 and 38 show progress made by Dŵr Cymru Welsh Water and Hafren Dyfrdwy. There are eight at-risk tanks that have not been fully inspected in the past 10 years, a slight increase from the previous year. Seven of these tanks are covered by separate regulation 28(4) notices, and four require a new tank to be constructed before the existing tanks can be removed from service. A short-term measure in these notices is the use of remotely operated vehicle inspections to provide information on current internal tank condition and integrity.
Figure 37 – DWR tanks data
Figure 38 – HDC tanks data
Figure 39 shows a comparison with other companies in the industry in 2026. The tank inspections that Dŵr Cymru Welsh Water have completed since the regulation 28(4) notice was put in place in 2022 have greatly improved their position and they now rank fourth in terms of percentage of assets at risk.
Hafren Dyfrdwy rank 14th in the industry in 2026. Although the overall number of tanks overdue an inspection has decreased, their overall ranking within the industry has not improved. This slow progress can be partially explained by the longer time frame over which it will take to construct the new tanks which are required in to remove four tanks overdue for inspection.