- 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
Research publications
Five research projects were published in 2025. A summary of each is included below.
Effectiveness of Water Treatment Processes in the removal of Endocrine Disrupting Compounds (EDCs)
This project concluded that endocrine disrupting chemicals were present in source waters supplying all three drinking water treatment works investigated, although the concentration were highly variable spatially and temporally. Most substances were not detected at concentrations above analytical limits of detection, indicating generally low prevalence. Where detections occurred, steroids and nonylphenol were consistently identified, aligning with historical monitoring data. A key conclusion was the identification of Di‑Isobutyl Phthalate (DIBP) in approximately half of all samples, representing the first quantitative evidence of its widespread presence in drinking water sources.
Due to the low frequency of positive detections and limited sample size, the study concluded that treatment removal efficacy could not be quantified with statistical confidence. Although DIBP removal appeared more consistent at the site employing slow sand filtration, this observation could not be robustly substantiated. Overall, the project concluded that existing monitoring approaches are insufficient to draw firm conclusions on treatment performance for EDCs. The absence of a health‑based guideline value for DIBP was identified as a significant regulatory gap, highlighting the need for further toxicological assessment and improved monitoring to better support future risk management
Bench-Scale and Pilot-Scale Water Treatment Efficacy Studies of PFAS Removal
This project concluded that the effectiveness of treatment processes for PFAS removal varies significantly depending on PFAS chain length, chemical structure and treatment technology. Adsorptive processes such as granular activated carbon and ion exchange were found to be effective for longer‑chain PFAS but consistently less effective for short‑chain compounds, with PFAS breakthrough early in testing. Ion exchange demonstrated greater capacity and longer operational performance than granular activated carbon, although both were influenced by source water quality.
Membrane processes, particularly nanofiltration and reverse osmosis, achieved the highest removal efficiencies, with reduction rates of up to 99% for many PFAS and greater than 80% for short‑chain compounds. Nanofiltration was identified as preferable to reverse osmosis due to comparable removal performance at lower operating pressures. Advanced oxidation and reduction processes were generally ineffective at the doses tested, while coagulation achieved only modest removal. The study concluded that pilot‑scale testing should focus on granular activated carbon, ion exchange, surface‑modified clays and nanofiltration to determine their operational feasibility at full scale.
Organophosphorus Flame Retardants – Risk to Drinking Water in England and Wales – Phase 2
This project concluded that organophosphorus flame retardants are detectable in both raw and treated drinking waters in England and Wales, although concentrations are generally low. Tri(2‑ethylhexyl) phosphate was identified as the most frequently detected compound and was present at the highest concentrations across monitored sites. Removal efficacy varied substantially between substances and treatment works, indicating inconsistent performance of conventional treatment processes.
Human health risk assessment concluded that exposure to the monitored flame retardants via drinking water is unlikely to pose an appreciable risk to human health under current conditions. However, the study identified significant uncertainty regarding usage for flame retardants in the UK, which limits confidence in exposure assessments. The project concluded that improved data on use, catchment risk and targeted monitoring of the most frequently detected compounds would significantly enhance understanding of potential future risks to water supplies.
Disinfection technology and alternative disinfection for commercial water
This project confirmed that the most widely used disinfection technologies in England and Wales are UV treatment and sodium hypochlorite, reflecting their effectiveness and operational familiarity.
The analysis concluded that hypochlorite solution offers the most balanced overall disinfection performance, particularly in terms of microbial removal efficacy, cost and asset management, despite its potential to form disinfection by‑products. UV disinfection ranked second but was associated with operational complexity. Chloramination and ceramic candle filters were concluded to be unsuitable as standalone disinfectants. Assessment of international practice identified ultrafiltration, mixed oxidant solutions and peracetic acid as warranting further investigation, while bromine was identified as requiring caution due to uncertainties regarding by‑product formation and health impacts.
Cryptosporidium – Review of the reports of the group of experts, literature and events
A review of previous expert guidance, combined with analysis of Cryptosporidium events in England and Wales between 2005 and 2022, demonstrated that failures do not arise from a single dominant cause. Instead, events were most commonly associated with insufficient treatment in relation to catchment risk, failures or deficiencies in assets, and weaknesses in operational procedures or staff training.
The project further concluded that while regulatory frameworks and guidance have evolved, continued vigilance is required across the full water supply system, from catchment to consumer. A wide range of monitoring and detection options are now available, including surrogate measures such as turbidity and particle counting, as well as direct detection methods using oocyst counts and molecular techniques. Emerging detection technologies were identified as offering potential future benefits, although their role in routine regulatory monitoring requires further evaluation.
In terms of treatment, the review concluded that multiple effective barriers are available, including physical removal, ozonation and ultraviolet disinfection. Newer technologies, such as ballasted clarification and ceramic membranes, were identified as particularly promising based on recent large‑scale UK installations. Overall, the project concluded that effective Cryptosporidium control relies on a systems‑based approach integrating catchment management, resilient treatment design, robust asset maintenance and competent operational practice, supported by up‑to‑date evidence and stakeholder engagement.
Chief Inspector’s Expert Group – Governance framework for rainwater harvesting and greywater reuse systems
England and Wales are increasingly facing an acute water scarcity challenge. The Environment Agency has predicted a demand gap of five billion litres per day by 2055 and tackling that requires action on multiple fronts, including making smarter use of the water we already have. In 2025, the Chief Inspector’s Expert Group produced this report: https://www.dwi.gov.uk/governance-framework-for-rainwater-harvesting-and-greywater-reuse-systems-report-published/. The report sets out how rainwater harvesting and greywater reuse (collecting water for uses such as toilet flushing, garden irrigation and laundry) can play an important role in reducing demand on our drinking water supply, whilst keeping public health firmly protected. Key findings include:
- Up to 22% of household water use goes on toilet flushing alone – all of which could safely use harvested rainwater or greywater instead of drinking water.
- Mandatory accreditation for water reuse installers and contractors (similar to the Gas Safe Register) would give the sector the credibility and consistency it needs to grow safely.
- As the technical experts in drinking water safety, we are committed to building public confidence in water reuse and this report provides the evidence base to show it can be done safely and effectively.
- Countries such as Germany and Belgium have safely practiced rainwater harvesting for over 20 years – there is a clear and well-trodden path for England and Wales to follow.
There are ten recommendations and the Inspectorate is working with others to take the work forward.