- 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
Enforcement, transformation and recommendations
Enforcement – England 2025
The Inspectorate publishes the drinking water quality legal instruments on its website under company improvement programmes. Security (SEMD and NIS) legal instruments are considered sensitive and therefore are not published in the public domain. The table below summarises the total legal instruments served in 2025.
| Type of legal instrument | Number of legal instruments | Companies |
|---|---|---|
| Regulation 21(3) Notice for the protection of health in public buildings | 1 | Thames Water |
| Regulation 27(4) Notice for improvements to water safety plans | 3 | South East Water (1), South Staffordshire Water (2) |
| Regulation 28(4) Notice relating to risks identified in water safety plans | 87 | Anglian Water (21), Northumbrian, Essex and Suffolk Water (12), South East Water (33), Southern Water (8), South Staffordshire Water (1), South West Water (5), Thames Water (5), United Utilities (2) |
| Final enforcement order under section 18 of the Water Industry Act for drinking water quality risks. | 1 | Southern Water |
| Undertaking accepted under section 19 of the Water Industry Act for drinking water quality risks. | 2 | Severn Trent Water (1), Thames Water (1) |
| Regulation 17 Notice for improvements under the Network and Information Systems Regulations. | 2 | Northumbrian Water (1), Portsmouth Water (1) |
| Undertaking accepted under section 19 of the Water Industry Act for SEMD improvements. | 3 | County Water (1), South East Water (1), Southern Water (1) |
| Formally acknowledged improvement actions* | 10 | Anglian Water (2), Southern Water (1), Wessex Water (7) |
*Acknowledged improvement actions are not legal instruments and as such, have no legal status. They are a set of actions that the company set out are being delivered and which the regulator (the Inspectorate in this case) formally acknowledges. They are used for improvement schemes, that the Inspectorate has commended for support, but which do not meet the threshold for formal enforcement.
Details of the new enforcement served in the first half of 2025 was published in the interim report, therefore details of new enforcement from the second half of the year follow.
Enforcement served in England, in the second half of 2025
Notices served under regulation 21(3)
A notice under regulation 21(3) was served on Thames Water following persistent lead exceedances at a property. Initial sampling in March 2024 recorded concentrations above the parametric value, and although partial pipe replacement was undertaken, subsequent monitoring confirmed that a residual lead risk remained. Given that the risk had not been adequately mitigated, and in line with the enforcement policy, the Inspectorate required the company to exercise its powers under section 75 of the Water Industry Act to protect consumers.
Notices served under regulation 27(4)
Several notices were served where companies had failed to establish or maintain adequate risk assessments. South Staffordshire Water was required to complete risk assessments for a new non-potable supply at Eddington, ensuring full compliance with regulatory requirements where water is supplied for domestic use.
Deficiencies in air valve risk assessment were also identified across multiple companies. South East Water and South Staffordshire Water were both subject to regulation 27(4) notices requiring the development and implementation of risk assessments covering air valves across treatment works, distribution systems, service reservoirs and water supply zones. These notices reflect the importance of fully embedded Drinking Water Safety Plans that account for all critical assets and associated risks.
Notices served under regulation 28(4)
A significant number of regulation 28(4) notices were served to address risks to wholesomeness across treatment works, distribution systems, and catchments.
At Sawston Mill, a replacement notice was served on South Staffordshire Water following early breakthrough of short-chain PFAS through GAC media. A revised long-term scheme has been put in place to address contamination associated with the Duxford Airfield borehole, benefiting approximately 135,050 consumers.
Northumbrian Water received a notice requiring improvements to clarifier operation and supernatant return at Mosswood works, where audit findings identified unacceptable risks due to high turbidity return flows and the inability to safely isolate assets for maintenance.
South East Water was subject to multiple notices, including mains replacement following prolonged discolouration affecting consumers, and replacement notices for failure to meet inspection requirements at Blean No.2 and Crowborough No.3 reservoirs. Further urgent action was required at Pembury works, where a notice was served without consultation due to immediate risk, requiring installation of microfiltration. Failure to meet early reporting milestones led to escalation towards a Section 18 enforcement order.
Southern Water was served several notices following a chlorate exceedance at Brede works and delays in its groundwater hazard review programme. These included restrictions on operation where chlorate levels exceed 700 µg/L and multiple notices to complete outstanding hazard mitigation actions. Additionally, Itchingfield service reservoir was removed from an existing notice due to access constraints, with a long-term replacement solution now required.
South West Water was served a notice to address longstanding discolouration at Trevemper Road, where replacement of an unlined cast iron main has now delivered measurable improvements in water quality.
Thames Water was subject to further notices addressing multiple risks. Following Cryptosporidium detections at Taplow boreholes, a long-term filtration solution was required. In addition, a wider compliance issue was identified across 39 treatment works lacking adequate post-contact tank chlorine monitoring, prompting a large-scale programme of upgrades. Enforcement was also taken in relation to lead exceedances in the Bourton supply system, where evidence indicated broader systemic risk.
United Utilities was served a regulation 28(4) notice following a technical audit identifying significant deficiencies in air valve risk management, including gaps in inspection, maintenance, and strategic planning.
Section 18 Enforcement Orders
The Inspectorate made a Section 18 Enforcement Order against Southern Water following failure to comply with existing regulation 28 notices. The order, effective until November 2033, ensures the delivery of key actions required to protect water quality and public health.
Section 19 Undertakings for SEMD
A company-wide Section 19 undertaking relating to SEMD was accepted following identification of security risks during an audit. The company committed to reviewing and strengthening its security risk assessment framework and physical assets.
Actions formally acknowledged
The Inspectorate acknowledged several planned improvement schemes, including disinfection upgrades proposed by Wessex Water across multiple sites. While regulatory compliance risks were currently low, these schemes will significantly improve future resilience.
Enforcement Developments
The Inspectorate continued to develop its enforcement processes, including expansion of the milestone and closure reporting portal to support change applications and annual reporting. Further enhancements are planned to align with NIS and SEMD frameworks.
Transformation Programmes
The Inspectorate continues to oversee transformation programmes across several companies to address systemic risks.
Southern Water remains the longest-running programme, with notable progress in 2025 including early completion of enforcement orders and significant delivery against its transformation plan. However, delays persist at some sites, and the company remains subject to a large number of active legal instruments.
Thames Water continues to demonstrate steady progress, including closure of key transformation notices and improvements in risk management. Engagement with the Inspectorate remains strong, supported by structured governance and high-quality reporting.
South West Water has progressed its transformation programme, completing key notices and improving engagement and performance, although challenges remain, particularly in the Isles of Scilly.
Northumbrian Water continues its transformation, with progress in closing legal instruments but ongoing requirements to deliver hazard review actions and strengthen asset management.
South East Water entered transformation following concerns around risk identification, asset resilience, and operational capability. The programme will focus on improving risk assessment, maintenance delivery, legal instrument management, and overall system resilience.
Overall, enforcement activity during this period reflects the Inspectorate’s continued focus on addressing systemic risk, improving asset resilience, and ensuring that companies take timely, effective, and sustained action to protect water quality and public health.
Enforcement Performance Metric
During 2025, the Inspectorate developed and tested a new metric to measure water company performance in respect of their obligations contained within legal instruments served by the Inspectorate. The metric assists the Inspectorate in directing its limited enforcement resource to those companies that require the most attention, as well as publicly demonstrating water company performance.
Every legal instrument served is scored, using a five by five matrix, which has a set of rules attached, which the inspectors follow for consistency.
The first score, assigned when the legal instrument is created, is the seriousness score. This score reflects the origins of the legal instruments and ranges from voluntary programmes, through routine enforcement action, to escalated and transformation enforcement. The criteria are listed in Table X, below.
| Seriousness | Seriousness score |
|---|---|
| Escalated enforcement – generally, enforcement orders but other forms too. | 5 |
| Further (additional) enforcement – “child” legal instruments, transformation legal instruments | 4 |
| Routine enforcement (realised breaches) – e.g. compliance assessments, events, regulation 26 breaches, data driven, consumer complaints, etc. | 3 |
| Routine enforcement (potential breaches) – e.g. likely to breach, risk of breach, audit findings, risk assessments, etc. | 2 |
| Proactive schemes – e.g. AMP schemes, voluntary undertakings, etc. | 1 |
The second score is a Red, Amber, Green (RAG) (expanded to include Amber + and Red +) status of the progress of the legal instrument. This score is assigned when the legal instrument is first created, but is changed, as required, throughout its lifetime based on the progress of delivery. The criteria are listed in Table X below.
RAG scores assigned to legal instruments
Red+ (5)
- The Inspectorate have rejected a change application for date extensions to the completion date of the legal instrument.
- Any delays that affect the end date of the legal instrument.
- Once a notice is in Red+ status, it can only ever recover to Amber +.
Red (4)
- The most recently submitted milestone is delayed or was delivered late.
- The most recently submitted milestone is insufficiently evidenced or incomplete (this is where a report is rejected entirely. Does not apply for routine follow-up questions).
- The Inspectorate have been notified that a future intermediate milestone is going to be delayed and there is no way the company can meet it.
- The Inspectorate have rejected a change application for date extensions for intermediate milestones.
- Last-minute notification of not going to meet targets, when clearly company have known for some time.
- Missed completion report deadline.
- Red applies until the next milestone is received, when the score may reduce to Amber or Amber +.
Amber+ (3)
- Escalated enforcement (see table above) always begins at Amber+
- New child legal instrument from a delayed legal instrument begins at Amber + (for example an individual service reservoir (SR) being removed from a wider SR notice).
- Change application has been submitted and accepted, with a new final delivery date.
- Legal instrument was previously at Red+ status, but company have resolved issues and improved management of notice.
- Cannot go lower than Amber+ once here.
Amber (2)
- Intermediate delay which does not affect the final date of legal instrument.
- There have been delayed/late milestones, but scheme is now on track.
- Previously red, but company have resolved the issues and improved the management of the legal instrument.
- Cannot go lower than Amber once here.
Green (1)
- Default option for all new legal instruments.
- All milestones are on target or completed on time.
- Change of solution which does not affect the final delivery date (ie the company have found a cheaper or quicker way of delivering the scheme within the notice period.)
- The Inspectorate direct a future change to a scheme (for example, the publishing of new PFAS guidance, which affects PFAS undertakings)
- DWI have initiated a change.
- Small administration changes (such as an annex update to a discolouration notice).
- Cannot return to green once amber or red.
The metric is then calculated in a similar manner to the recommendations risk index. There is an acceptance that risk will always exist and the bigger the company (bigger catchment, more water treatment, more treated water storage, more kilometres of mains and more connections), the higher the residual risk. Total scores for each company are compared to those of the whole sector and normalised based on the proportion of overall population supplied to give an expected score for each company. The expected scores are then plotted against actual scores, for each company, using a linear regression. The upper 95% confidence value line is added, to highlight where there are statistical outliers, producing the graph shown below (Figure XX), which is the Enforcement Performance Metric for the end of 2025.
Figure 58 – Enforcement Performance Metric 2025
During the first half of 2025, we gave an amnesty to companies on NIS and SEMD legal instruments, as the reporting processes and requirements were all new to these areas. We sought to support, educate and advise, rather than reprimand where items were delivered late or incomplete. Whilst we are always available to advise companies, the period of grace has now ended and the NIS and SEMD legal instruments will be scored appropriately. At the present time, NIS and SEMD legal instruments are included with the drinking water quality enforcement into a single measure. This is due to there being only a small number of those legal instruments, compared to the overall number. This will be reviewed in the future, and they may be separated out if there is a benefit to doing so.
The metric shows that as of 31 December 2025, South East Water, Southern Water, South West Water and Anglian Water are the outlier companies. South East Water and Anglian Water both have a high number of notices served for individual service reservoirs and other treated water tanks after failing to complete the required inspections under their “all tanks” notices. These notices all score highly as they represent a failure to deliver on previous legal instruments. As these notices are delivered (tanks are inspected and repaired), they will be revoked and the scores will decrease accordingly. South East Water also has other legal instruments with high RAG scores due to the late reporting of milestones. The management of its legal instrument obligations has been raised with the company and will for a key part of its transformation programme.
Southern Water has historically failed to deliver its transformation notices on time, which has resulted in multiple final enforcement orders being made on the company which attract high scores. The company also have several “child” notices resulting from previous transformation notices, which will also score highly. The company do have a large number of closure reports due in 2026 and 2027, so we look forward to their score decreasing over the next two years, as we are able to close or revoke completed legal instruments.
South West Water has five highly scoring legal instruments for the Isles of Scilly, which are severely delayed, alongside some delays on other legal instruments. This is sufficient to push them above the 95% confidence interval line. With the length of delays on the island notices, this position is not likely to be fixed for some time.
Recommendations
In 2025, the Inspectorate issued 756 recommendations completing the assessment of 667 compared to 836 recommendations to water companies and new appointments and variations in 2024. This remained a substantial level of regulatory intervention and was higher than the 714 recommendations issued in 2023 and 564 issued in 2022. The company-level data shows that recommendations continued to be distributed across most companies, with the highest numbers issued to Thames Water Utilities Ltd (92), Dŵr Cymru Welsh Water (83), Severn Trent Water Ltd (69), Anglian Water Services Ltd (59), Northumbrian Essex and Suffolk Water (56), and United Utilities Water Ltd (51). These companies accounted for a significant proportion of the total recommendations, although recommendations were also made across a wide range of other water companies and NAVs. This indicates that the issues identified through the Inspectorate’s regulatory activity were sector-wide and not confined to a small number of companies.
| Company | Number of Recommendations |
|---|---|
| Advanced Water Infrastructure Networks | 3 |
| Affinity Water Ltd | 36 |
| Albion Water Ltd | 3 |
| Anglian Water Services Ltd | 59 |
| Bristol Water Plc | 13 |
| Cambridge Water Company Plc | 13 |
| Dwr Cymru Welsh Water | 83 |
| ESP Water Limited | 4 |
| Hafren Dyfrdwy | 6 |
| Independent Water Networks Limited | 31 |
| Isles of Scilly | 1 |
| Last Mile Water Limited | 15 |
| Leep Networks Water Ltd | 15 |
| MUA Water Ltd | 3 |
| Matrix Water | 2 |
| Northumbrian Essex and Suffolk Water | 56 |
| Portsmouth Water Ltd | 5 |
| SES Water | 6 |
| Severn Trent Water Ltd | 69 |
| South East Water Ltd | 40 |
| South Staffordshire Water Plc | 24 |
| South West and Bournemouth Water | 23 |
| Southern Water Services Ltd | 38 |
| Thames Water Utilities Ltd | 92 |
| United Utilities Water Ltd | 51 |
| Veolia Water Projects Ltd | 5 |
| Wessex Water Services Ltd | 15 |
| Yorkshire Water Services Ltd | 45 |
The distribution of recommendations reflects both the scale and complexity of company operations and the nature of the issues identified through audits, event investigations and other regulatory activity. Regulatory breaches remained the principal reason for making recommendations, particularly where a company had failed to comply with statutory requirements in circumstances that resulted, or could have resulted, in a risk to the wholesomeness or sufficiency of drinking water supplies.
| Recommendation Type | Sum |
|---|---|
| Deficiencies with risk assessment | 119 |
| Deficiency relating to policy/procedure | 103 |
| Inadequate investigations | 82 |
| Deficiency relating to service reservoir or network management/operation/maintenance | 61 |
| Issues with sampling (appropriateness or accuracy) | 34 |
| Deficiencies with consumer communication | 30 |
| Deficiencies with other treatment operation / maintenance | 29 |
| Deficiencies with disinfection operation / maintenance | 26 |
| Inadequate follow up sampling | 25 |
| Issues with provision of inaccurate information | 21 |
Risk assessment failings were the most common area of non-compliance, with 119 recommendations These recommendations reflected shortcomings that the Inspectorate considered to have been within company control and which should have been identified, assessed and managed through effective drinking water safety planning. Failings associated with policy and procedures accounted for 103 recommendations, while investigation-related requirements accounted for 82. Deficiency relating to service reservoir or network management/ operation/ maintenance Disinfection and treatment failings resulted in 61 recommendations, underlining the continued importance of basic processes, effective operational monitoring and timely response to deterioration in source or treated water quality.
Figure 58 – Assessment and response of recommendations given to each company in 2025
This year an assessment of the average assessment and response score provides insight to those companies which are either creating serious recommendations or not responding adequately to recommendations driving up the outcome on the recommendations risk index seen in the graph below.
