Data return findings
During 2025, the Inspectorate gathered data through the annual data return, which is a statutory reporting requirement of local authorities under regulation 14 of the Regulations.
Local authorities must keep records of every private supply in its area and submit these to the Inspectorate by 31 January each year. Local authorities bear the sole obligation for reporting data and information to the Secretary of State under the requirements of regulation 14 and schedule 4 of the Regulations. Therefore, the Inspectorate will not accept data or information from third parties where no agreement is in place. It is also a regulatory requirement for sampling and analysis to be accredited to ensure the integrity of the data.
Meeting the standards for wholesomeness
Under the Regulations, drinking water should be ‘wholesome’ meaning it does not contain any microorganism, parasite, or substance at a concentration or value that exceeds limit values (in Part 1 of Schedule 1) or would constitute a potential danger to human health. In 2025, 2.21% (5,979 out of 271,024) tests reported by local authorities in England were found not to be meeting one or more of the standards for wholesomeness. Figure 3 shows that overall, there has been a reduction in tests failing the regulatory standards. However, these figures must be caveated because the overall number of tests carried out is below that which would be expected for the number of private water supplies recorded in England.
Figure 3 – Number of tests from 2014 to 2025 with failure percentages
Escherichia coli (E. coli) and Enterococci are indicators of faecal contamination. The percentage of samples which were reported to be contaminated by E. coli and Enterococci in the period 2015-2025, is shown in Figure 3. From the samples reported in 2025:
- At least 4.08% of tests contained faecal contamination,
- 3.67% of samples tested contained E. coli and,
- 4.56% of samples tested contained Enterococci.
These organisms are almost exclusively found in faeces, indicating a potential danger to the health of those drinking this water.
It must be noted that the testing regime is not uniform year on year, with significant under-reporting. The number of consumers using private water supplies where E. coli and/or Enterococci have been found equates to 451 supplies, indicating more than 16,000 people drinking water at risk of faecal contamination. In comparison to public supplies, which are 99.98% compliant with water quality standards.
| Microbiological parameters | 2023 (%) | 2024 (%) | 2025 (%) |
|---|---|---|---|
| E. coli | 4.84% | 4.89% | 3.67% |
| Coliform bacteria | 11.55% | 10.50% | 7.42% |
| Enterococci | 5.90% | 5.74% | 4.56% |
| Clostridium perfringens | 8.06% | 7.16% | 3.06% |
Figure 4 – Percentage failure for E. coli and Enterococci
Monitoring frequencies and sampling shortfalls
Regular testing, annually, every five years or as informed by risk assessment, is essential to assess water quality and the effectiveness of control measures. At an aggregate scale, it is clear that private water supplies are not being tested at the frequencies required by the Regulations. It is vitally important for a supply’s regulatory testing regime to be determined and then met.
This validation monitoring provides a baseline to measure the overall quality of the supply and the effectiveness of any mitigation measures. Other sampling, which could be called ‘investigatory’, can be recorded as such on the annual data return and is often undertaken following programmed sampling to investigate results which deviate from an established baseline, are near to, or exceed the standards.
In 2025, local authorities carried out 271,024 analyses of private water supplies samples. Figure xxx shows a general increase in the number of samples taken since 2014, with 2020 representing an exceptional year due to the impact of the pandemic. There has been a gradual decline in the number of tests reported to the Inspectorate since 2022, increasing the sampling shortfall for private water supplies.
Due to the risks associated with private water supplies, increasing resources to reduce the shortfall would be beneficial to protecting public health.
Figure 5 – Number of samples taken for private water supplies
Risk assessment and risk management
One of the key principles of the Regulations is to carry out a risk assessment to establish whether there is a potential risk of supplying water that may be unwholesome or would constitute a potential danger to human health.
Each local authority must carry out or review a risk assessment of each qualifying private water supply system in its area at least every five years, or earlier if it is considered that the supply presents a risk.
The Inspectorate has developed a set of risk assessment tools to help local authorities comply with their duties under regulation 6. These can be found on the Inspectorate’s risk assessment web page – Risk Assessment tools and tips – Drinking Water Inspectorate.
Local authorities report information on risk assessments and enforcement action to the Secretary of State (in practice the Inspectorate) in two ways; in the annual data return, and through summaries of risk assessments. Also, throughout the year, local authorities must submit to the Secretary of State copies of notices served on supply owners for high-risk supplies or failing parameters.
To date, the numbers stated in the annual data returns have never matched the number of documents received, with under-submission of risk assessment summaries and notices a consistent issue. Local authorities are reminded that documents can either be redacted or sent by a secure file transfer to preserve data privacy.
Figure 6 highlights that local authorities are not making significant progress in moving towards 100% coverage of risk assessments. For the past three years, most private water supplies that should have been risk assessed, either have never been, or were risk assessed more than five years ago. This demonstrates deficiencies in the regulatory governance of private water supplies which were highlighted in the Inspectorate’s research project findings – Impact and future of the regulatory model and legislative framework surrounding private water supplies in England and Wales – Drinking Water Inspectorate.
| Supply type | In-date (within last 5 years) | Out-of-date (>5 years since completion | No record of risk assessment | Total number of risk assessments | Risk assessments in date |
|---|---|---|---|---|---|
| Regulation 8 | 125 | 37 | 292 | 454 | 27.5% |
| Regulation 9 | 4,509 | 2,352 | 1,310 | 8,171 | 55.2% |
| Regulation 10 (shared) | 1,365 | 1,792 | 1,657 | 4,814 | 28.4% |
| Regulation 11 (Wales) | 204 | 1,189 | 0 | 1,393 | 14.6% |
| Total | 6,203 | 5,370 | 3,259 | 14,832 | 41.8% |
Figure 6 – Risk assessments carried out
Summary of data submitted to the Inspectorate – Microbiological failures
During 2025, more than one in 25 supplies in England are unfit for human consumption and pose a risk to health as they contain E. coli and Enterococci. Whilst coliforms are not always a direct indicator of faecal contamination, they still indicate that there is a route for contamination to enter the supply and that contamination has not been removed by treatment. Protection of supplies from contamination is critical to protecting public health.
Should a supply be found to contain the presence of faecal indicators, the local authority is obligated to investigate in accordance with regulation 16 of the Regulations.
Summary of data submitted to the Inspectorate – Chemical failures
Lead
Lead was detected in 2.35% of tests. Lead is a neurotoxin that particularly affects children but can also cause health effects in adults through long term accumulation including chronic kidney disease, raised blood pressure, and cardiovascular disease. Where lead is detected above the regulatory standard, local authorities must serve a regulation 18 notice to secure actions to protect the health of the consumers. The most robust long-term solution is the removal of any lead pipework, lead-containing fittings, and lead solder. The World Health Organization has recently published its refreshed technical brief on lead, which can be found on its website. The Inspectorate has published guidance on lead in private water supplies on its website – Lead in private water supplies – Drinking Water Inspectorate.
Nickel
Nickel was detected in 2.24% of tests, Nickel is largely detected because of nickel plated domestic fittings such as taps. Sometimes the source is not as obvious and could be under sink mixers and temperature regulators. Consumers should be advised to replace these fittings where failures of the standard occur.
Iron, manganese, and aluminium
Iron, manganese, and aluminium failed standards in 4.05%, 4.56% and 0.92% of tests respectively. All these metals can be found naturally occurring in source waters. Local authorities should consult with UKHSA to determine whether the concentration of these metals poses an immediate danger to health, and if so, must serve a regulation 18 notice. Should the presence of these metals not be deemed a potential danger to health, local authorities can still act under section 80 of the Water Industry Act 1991 (the Act) to compel the relevant persons to make the supply wholesome and acceptable for all domestic purposes, which includes washing and domestic laundry.
Turbidity and colour
Turbidity and colour were recorded at concentrations above the standards in 1.11% and 1.36% of tests respectively. Turbidity can reduce the effectiveness of disinfection so a detection of turbidity in excess of the standard should trigger an investigation to determine the cause, followed by the appropriate course of action under regulation 18 or section 80. Colour detections are usually caused by compounds which arise from the catchment of the source waters and can be removed by suitable treatment processes.
A short-term increase in colour and/or turbidity can be a result of high rainfall mobilising humic and fulvic substances in source waters. If these short-term occurrences become more frequent, this may be a result of long-term changes in weather patterns, and may indicate that additional treatment could be required in the future.
| Chemical parameters | 2023 | 2024 | 2025 |
|---|---|---|---|
| Odour | 4.37% | 4.01% | 1.81% |
| Taste | 3.78% | 3.94% | 0.58% |
| Manganese | 4.42% | 4.79% | 6.28% |
| Iron | 4.15% | 3.81% | 2.73% |
| Aluminium | 1.11% | 1.14% | 1.33% |
| Turbidity | 0.94% | 0.96% | 1.24% |
| Colour | 1.15% | 1.52% | 1.03% |
| Lead | 2.69% | 2.38% | 3.48% |
| Nickel | 3.73% | 2.36% | 1.49% |
| Pesticides | 0.17% | 0.08% | – |
| Fluoride | 1.01% | 1.69% | – |
| Nitrate | 6.54% | 8.42% | 0.50% |
| Nitrite | 1.05% | 1.34% | 1.23% |
PFAS
The data return suggests that just 23 supplies have an in-date risk assessment for PFAS. The Environment Agency has continued to write to the local authorities, and the relevant person/s when a private water supply on its groundwater monitoring programme is found to contain PFAS in concentrations above the limit of detection. Local authorities are encouraged to refer to the Inspectorate’s guidance on PFAS, which was updated in 2025 – PFAS Guidance.
In the data submitted by local authorities in 2025, 76 out of 463 tests contained PFAS above the Inspectorate’s guidance value of 0.1 µg/L. 74 of these samples were collected from a single site spilt between three different sampling visits. This is an exceedance rate of 16.41%, significantly more orders of magnitude than the failure rate for public supplies. Fortunately, the main failing site has granular activated carbon (GAC) treatment installed to mitigate the impact of the PFAS and its efficacy is carefully monitored by the company operating the site.
The Inspectorate encourages local authorities to submit PFAS data in annual data submissions. PFAS samples will be regarded as ‘investigatory’ samples as tests are not required under the Regulations. Local authorities assessing PFAS risk may wish to consult the Environment Agency open data which holds PFAS test data for its groundwater monitoring sites. Some of the sites are private water supplies, and others may be located near to private water supplies. The quantitative results would be most useful, and grid references of the sample points are included.
The Inspectorate has published guidance on PFAS in private water supplies on its website – Poly and Perfluorinated Alkyl Substances (PFAS) – Drinking Water Inspectorate.
In 2025, the Inspectorate published research on efficacy studies of PFAS removal which may be of benefit to local authorities and relevant persons – Bench-Scale and Pilot-Scale Water Treatment Efficacy Studies of PFAS Removal – Drinking Water Inspectorate.
Enforcement
Local authorities are required to send notices served under the legislation to the Secretary of State (in practice the Inspectorate) in accordance with regulation 18 where supplies are a potential danger to human health. They may also serve notices under section 80 of The Water Industry Act 1991 (the Act) where supplies are unwholesome and or insufficient.
The Inspectorate has been notified of 149 notices served in 2025; 126 served under regulation 18 and 23 served under section 80.
Most notices are served in response to a failure of a microbiological standard, with a small minority for failures of other standards. In 2025, according to the data return, 232 notices were issued for failures of water quality standards, this discrepancy in the notices served and that reported in the data return highlights the issue with inaccurate data reporting.
Local authorities still appear to be predominantly reacting to sample results, rather than proactively eliminating the problems that could result in a test failure. The use of a proactive risk assessment, and if necessary, a notice, is to protect users before unwholesome or unsafe drinking water occurs.
Table 5 shows the number and primary parameter driver for the 232 notices issued, with some notices covering multiple parameters.
| Parameter name | Number of notices served |
|---|---|
| Coliform bacteria | 137 |
| E. coli bacteria | 112 |
| Enterococci bacteria | 88 |
| Clostridium perfringens bacteria | 39 |
| Nitrate | 33 |
| Colony counts after 3 days at 22°C | 29 |
| pH | 22 |
| Lead | 23 |
| Copper | 20 |
| Nitrite/Nitrate formula | 20 |
| Manganese | 18 |
| Colour | 16 |
| Iron | 16 |
| Arsenic | 13 |
| Turbidity | 11 |
| Odour | 10 |
| Nickel | 8 |
| Taste | 6 |
| Aluminium | 5 |
| Colony counts after 48 hours at 37°C | 4 |
| Nitrogen (total) oxidised | 3 |
| Sodium | 3 |
| Antimony | 1 |
| Boron | 1 |
| Bromate | 1 |
| Chloride | 1 |
| Fluoride | 1 |
| Gross alpha (radioactivity) | 1 |
| Lead (dissolved) | 1 |
| Nitrite (total) | 1 |
| Sodium (dissolved) | 1 |
| Sulphate | 1 |
| Trichloromethane-Chloroform (total) | 1 |
| Trihalomethanes (total by calculation) | 1 |
| Total | 232 |