Data return findings
During 2024, the Inspectorate gathered data through the annual data return which is a statutory reporting requirement of local authorities.
The quality of water supplies from private water supplies in England
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.
For the reporting year 2024, a submission was received from 207 local authorities, which is six fewer than the previous year. Note that colony count test numbers have been removed from all years in this report’s charts.
In 2024, local authorities carried out 229,216 analyses of private water supplies samples. This is a decrease of 3.8% on the previous year and 6.61% less than the numbers taken in 2019 pre-pandemic. Figure 2.1 shows a general increase in samples taken since 2014, with 2020 representing an exceptional year due to the impact of the pandemic. There appears to be a gradual decline from the number of tests in 2022 to today, increasing the 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 2.1 Number of tests from 2014 to 2024
When analysing the test data to produce this report, the Inspectorate identified an anomaly. There was a much greater number of colony-count failures than previous years. The standard for colony counts (specifically three days at 22 degrees centigrade) which is an indicator parameter, is ‘no abnormal change’. There is therefore no ‘prescribed concentration or value’ (PCV). It is the responsibility of local authorities to determine what would be an abnormal change for any particular private water supply. An abnormal change may indicate a problem with the quality of the supply. In public supplies, it is not uncommon to see colony counts between tens and hundreds, which are a stable background levels for a supply or perhaps an asset such as a treated water reservoir within distribution. Investigating this anomaly further, the Inspectorate found that a problem with the validation macros of the data return Excel template meant it would not allow a colony count value of greater than zero (in effect a count of one or more) to be entered as a ‘pass’. Unfortunately, many local authorities decided the best course of action was to change these results to a ‘fail’ to eliminate the spreadsheet error. This was unnecessary, as the database validation routine was working correctly, and would have accepted these results as passing tests, had the Excel template been uploaded. The Inspectorate will investigate options to rectify this incorrect data with local authorities affected, during 2025. Due to this data error, colony count test data and information have been removed from charts and figures in this report.
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 the regulatory testing regime for a supply to be determined and then met each year, or every five years, as appropriate. This validation monitoring provides a baseline to measure the overall quality of those supplies and the effectiveness of mitigation measures. Other sampling, which could be called ‘investigatory’, can be recorded as such on the annual data return. Figure 2.2 illustrates the issue of incorrect testing frequencies for one parameter, E. coli. At regulation 9 supplies, E. coli should always be tested at the Group A frequency stipulated in the schedules to the Regulations. Samples taken as group A must be recorded in the data return as such.
In 2024, 44% of regulation 9 supplies were tested at the correct frequency for E. coli according to the volume supplied. This is an improvement on 34.3% in 2023. A further 9% were tested at a higher frequency than that required by the Regulations. However, the remaining 47% of supplies had fewer tests than required by the Regulations, 4% of which were under-sampled and 43% not sampled at all. In 2023, 53% of supplies were not tested for E. coli at all, so there has been a welcome step-change in local authorities testing regulation 9 supplies which, as large supplies that may also be used in commercial or public activities, are the supplies which pose the most potential for risk to public health.
Figure 2.2 Regulation 9 supplies tested for E. coli at Group A frequency
Third party risk assessments and sampling
The Inspectorate attends various regular meetings and events each year. A common point of discussion at these meetings is risk assessments and test data from third parties. The Inspectorate can confirm that it does not receive data or any other information on private water supplies from third parties. The only data submission process in place is the one managed directly with local authorities.
If local authorities are using third parties to conduct private water supplies sampling and testing, the requirement of schedule 3 part 1(4) of the Regulations for an agreement (contract) to be in place must be met. This contract between the local authority and the provider must ensure that the requirements of the Regulations are met, and that any breach of those requirements is reported to the local authority within 28 days.
While there is no similar direct provision in the Regulations for local authorities to use third parties to conduct risk assessments, the very nature of conducting a holistic risk assessment means drawing on the information and knowledge of others who are informed about the supply. Though, third parties may be major contributors to the risk assessment process, local authorities still carry the responsibility for the risk assessment overall, and are the only entity empowered to act in response to the risk assessment’s conclusions.
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. Regulation 8 supplies would be the most common supply type that may involve a third party. Some of these onward supplies serve a large number of consumers, with the third-party distributors often being large organisations or companies. The Inspectorate has been involved in informal discussions when local authorities have cited that these third parties either refuse to share their test data or assure the local authority that test data is being shared with the Inspectorate. As the Inspectorate does not receive any data or information from third parties, this indicates a potentially large data gap which is likely due to missing third-party data.
Table 1 A summary of the percentage of samples failing for various microbiological and chemical parameters.
|
Microbiological parameters | ||
| 2023 | 2024 | |
|
E. coli |
4.93 |
4.46 |
|
Coliform bacteria |
13.20 |
10.31 |
|
Enterococci |
5.98 |
5.40 |
|
Clostridium perfringens |
5.05 |
4.68 |
|
Chemical parameters | ||
|
2023 |
2024 | |
|
Odour |
4.37 |
4.01 |
|
Taste |
3.78 |
3.94 |
|
Manganese |
4.42 |
4.79 |
|
Iron |
4.15 |
3.81 |
|
Aluminium |
1.11 |
1.14 |
|
Turbidity |
0.94 |
0.96 |
|
Colour |
1.15 |
1.52 |
|
Lead |
2.69 |
2.38 |
|
Nickel |
3.73 |
2.36 |
|
Pesticides |
0.17 |
0.08 |
|
Fluoride |
1.01 |
1.69 |
|
Nitrate |
6.54 |
8.42 |
|
Nitrite |
1.05 |
1.34 |
|
Others |
2.90 |
3.04 |
Microbiological failures
The detection of specific indicator micro-organisms means that a supply is contaminated. When E. coli, Enterococci and to a lesser extent Clostridium perfringens are found, this suggests that the contamination may be faecal in origin. Faeces often carry micro-organisms including bacteria, viruses and parasites which are harmful to health and when a faecal indicator is found, this water should not be consumed.
Table 1 shows that during 2024, in England more than one in 25 supplies may be unfit for consumption and pose a risk to health containing E. coli. 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. This was found in one in 10 tests. Protection of supplies from contamination is critical to protecting public health. Should a supply be found to contain the presence of faecal matter, the local authority is obligated to investigate in accordance with regulation 16 of the Regulations.
Other failures
Taste and odour failures could be caused by the quality of the source water or develop as water passes though the distribution system. How consumers describe the taste or odour can help identify the cause with descriptions such as ‘earthy’ or ‘musty’ pointing to possible algal problems in the source water and ‘woody/pencil shavings’ suggesting the presence of black alkathene pipework, to use a couple of examples.
Lead and nickel were detected in 2.38% and 2.36% of tests respectively. For lead this is a decrease compared with 2.69% in 2023, 3.63% in 2022. Lead is a neurotoxin that particularly affects children and can cause health effects in adults including chronic kidney disease, raised blood pressure and cardiovascular disease. Where lead is detected above the 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 their refreshed technical brief on lead, which can be found on its website.
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 can be seen to have failed standards in 3.81%, 4.79% and 1.14% of tests respectively. All these metals can be found naturally occurring in sources waters. Local authorities should consult with UKHSA to determine whether the concentration of these metals pose 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 to compel the relevant persons to make the supply wholesome and acceptable for all domestic purposes which includes washing and laundry.
Turbidity and colour are seen to have been found in concentrations above the standards in 0.96% and 1.52% 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 of the Water Industry Act 1991 (the Act) to carry out improvement actions. 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 substances in source waters. If these short-term occurrences become more frequent, this may be a result of long-term changes in weather patterns.
PFAS
The data return suggests that 465 supplies have been risk assessed, including the risk posed by PFAS. This is reduction on last year when 625 were said to have PFAS risk assessments.
The Environment Agency has continued to write to local authorities and supply owners/users when a private water supply on its ground water 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, and to investigate these supplies to evaluate the level of risk posed to consumers.
Within the test data submitted by local authorities, there were three supplies with concentrations of PFAS within tiers 2 or 3 of the Inspectorate’s guidance, requiring investigation and remedial action. One supply is known and is a food production premises. The Inspectorate has liaised with the local authority regarding this supply, and it is active in the supplies’ catchment area, with a good understanding of the risk. The other two sites have concentrations in tier 2. One is a regulation 10 shared supply in Adur and Worthing Council’s area which does not have a risk assessment that includes PFAS. The last risk assessment was completed in 2014 and therefore its five-yearly review is overdue. The other is a regulation 9 supply in Spelthorne Borough Council’s area, which did have a PFAS risk assessment conducted in 2024. 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.
Interpreting test results
Water sample results provide insight into the quality of water at the time the sample was taken and can act as an indication that further investigation is needed.
Local authorities submit sample results to the Secretary of State annually. A small subset of results provided each year exceed the regulatory limits by a significant magnitude. Not all of these figures have a commentary provided with them in the data return, which would be an opportunity to explain exceptional circumstances.
Five results for ammonium above 5 mg/L were received, 10 times above the regulatory limit.
Excess ammonium within distribution networks encourages the development of nitrifying bacteria, which can subsequently increase the concentrations of nitrite. Seven results above 10 mg/L of nitrite were reported. The limit at the consumer tap is 0.5 mg/L.
Nitrite is a health-based parameter as babies and younger children are susceptible to develop methaemoglobinaemia at concentrations of nitrite above the regulatory limit. Nitrite is an oxidant and so oxidises iron in haemoglobin (in blood) to methaemoglobin. This means that there is not enough iron in haemoglobin to transport oxygen in the body, resulting in symptoms such as a blue discolouration to the skin (known as cyanosis) and in severe cases, it can result in death.
There was one sample received for gross alpha, seven times the regulatory limit of 0.1 Bq/L. The regulatory limits on gross alpha and gross beta are in place due to the impact on indicative dose of some radionuclides. Some radionuclides will exceed indicative dose when they produce a gross alpha result of 0.1 Bq/L, which is why it is critical to understand the source of radioactivity once gross alpha or beta is exceeded. This is done through an indicative dose test (also known as speciation) which provides more detailed information so that decisions can be made regarding the health effect of the radioactivity as well as possible treatment.
Five samples taken from the same location for benzo[a]pyrene were reported as above 0.42 µg/L against a standard of 0.01 µg/L. A further sample over 400 µg/L was reported from a different site. Benzo[a]pyrene is present in the regulations because it is a carcinogen. Therefore, seeing multiple results above the limit at the same site is of concern. If multiple samples from different sources exceed the limit with no explanation from the risk assessment, the laboratory should be consulted for further advice on the validity of the results. Local authorities should also check to ensure that any qualifiers provided by the laboratory for the data are included in the annual data return as this can greatly affect the interpretation of any results.
Ten results over 100 µg/L were reported for lead. There is no safe level of lead with the best solution to the presence of lead pipework being its removal. Lead is also present in brass fittings to varying levels. An investigation should be undertaken by the local authority for all lead results above the regulatory limit and should be considered at values below that.
In England, a number of strontium results over 4000 µg/L were reported. There is no regulatory limit for strontium; however, strontium can be a radioactive element. The risk of radioactive strontium, which has a different health-based limit, should therefore be assessed through the risk assessment process. Risks from radioactivity should be discussed with UKHSA in England. The possibility of the presence of radioactive strontium would indicate the need for further radioactive testing.
Sixteen results over 20 NTU were provided for turbidity. Turbidity indicates how much the light reflects within a sample of water. The higher the turbidity, the more difficult it is to fully disinfect the water. This includes with ultraviolet light. For supplies with high turbidity the risk assessment should consider the effectiveness of disinfection and the risk of disinfection byproducts.
One sample in England returned a high result for vinyl chloride, which was hundreds of times the regulatory limit. This value is usually controlled by product specification, limiting the material in products coming into contact with water. Vinyl chloride monomer is used in the production of PCV (polyvinyl chloride). This is mostly used in plastic pipework, but it can also be formed from the breakdown of other chlorinated compounds, something which is often noted in water supplies close to landfills. Any results above or close to the regulatory limit for vinyl chloride should be fully investigated to ascertain the source of the increased monomer concentration as this compound is associated with various health risks.
Several results of the pesticide DDT were reported. DDT was banned in 1984 in the UK. To receive nine results at exactly the same concentration, six times the general pesticide limit, is extremely unusual. Any positive DDT result should be investigated as it would indicate a change to the catchment which has encouraged the release of pesticide which has been stored for decades. There may therefore be other catchment risks not revealed by the sampling regime.
Eleven fluoride results were reported of 150 mg/L or above. As well as being scientifically very improbable, these concentrations present a significant health risk and should have been investigated immediately, especially from a regulation 9 supply supplying food products to the general population.
However, the more likely explanation is that these results have been supplied in a different unit to those required by the regulatory data input. It is always important for local authorities to check the regulatory unit requirements prior to data submission as results may need to be converted prior to submission. Laboratories occasionally report some parameters in nanograms per litre when the regulatory limits are provided in micrograms per litre.
Risk assessments
In 2024, the percentage of private supplies which have an in-date risk assessment are:
• Private distribution systems (regulation 8 supplies) 25.5%.
• Large, commercial and public use (regulation 9 supplies) 45.9%.
• Small supplies (regulation 10 supplies) – 27.8%.
In total, 13,092 supplies require a risk assessment, and only 5,143 (39.3%) have one that has not expired. For all supply types other than single dwelling supplies, local authorities have been required to complete risk assessments since 2010. It is concerning that, 10 years after the introduction of this requirement, there is still a significant proportion (31.6%) where the risk assessment has exceeded the requirement for a five-yearly review and a critical 29.1% which have never had a risk assessment where users remain unsuspecting that their supply may contain faecal contamination.
In addition, supplies to untenanted single dwellings (regulation 10[3] supplies) are only risk assessed upon the owner’s request and 14.3% on a risk assessment programme have in-date risk assessments. Local authorities are reminded that once a supply to a single dwelling has been risk assessed the risk assessment must then be reviewed every five years.
In 2018, a change in the Regulations brought about the requirement for local authorities to provide a summary of the results of risk assessments to Ministers (in practice the Inspectorate) within 12 months of having carried out the assessment.
During 2024, the Inspectorate received 200 risk assessment summaries from 23 local authorities. This is an almost identical number as received during 2023. There are still 188 out of 211 local authorities in England that submitted data on private supplies who have not met the statutory reporting requirements regarding risk assessments in 2024. We would encourage local authorities to at least programme an annual exercise to submit the risk assessment summary pages to the Inspectorate, perhaps to coincide with the annual data return submission.
A review of the submitted risk assessment summaries suggest that some local authorities are only conducting reactive risk assessments following sample failures. Risk assessments and associated mitigation measures should be verified by sampling, and not the other way round. Data including sample results can be used to inform a risk-based prioritisation of risk assessments and it may be prudent to review risk assessments following sample failures. However, the risk assessment process must be a proactive one and not a process where risk assessments are only conducted where sample failures have occurred.
Protection of the source and the abstraction point were common root causes of risk identified as part of local authority risk assessments. The need for remedial actions to protect the source of a private supply from risk of contamination from livestock, slurry, pesticides, and septic tanks featured repeatedly on the summaries submitted to the Inspectorate. Similarly recurrent were actions required to secure spring chambers, headworks, and buildings from drainage issues, unauthorised access and vermin.
Ultraviolet (UV) systems are commonly used for disinfection in private water supply systems. The efficiency of UV systems used for disinfection are affected by the water quality and the flow rate through the system. High turbidity can shield pathogens from the UV dose and an improper unit for the required flow rate may result in an insufficient UV dose applied. Local authority assessors noted risks from a lack of maintenance, resilience and control in some systems. Common mitigations required the need for intensity monitors, alarms and shutdowns in case of unit/bulb failures, power interruptions, or high turbidity in the influent water which may inhibit UV disinfection. Such controls would reduce the risk of partially or non-disinfected water being available for consumption.
The absence of regular inspection, cleaning, and maintenance of water storage tanks was frequently flagged as a risk in the risk assessment summaries. For comparison, treated water tanks (storage reservoirs) are an integral part of public water supply networks. Water companies conduct external inspections annually to identify risks from ingress and contamination. Furthermore, water companies must conduct internal inspection, cleaning, and remedial maintenance at a frequency dependent on the risk and the quality of the influent water. Assets such as water tanks are not in stasis and require regular intervention to maintain operability.
Enforcement
Local authorities are required to serve notices served under the legislation to Ministers (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.
In 2024, the Inspectorate received 114 notices served under regulation 18 of the Regulations for supplies that were considered a potential danger to human health. The data return indicated that 231 had been served in 2024. Forty-seven notices were served under section 80 of the Act according to the data return, but only four were received by the Inspectorate.
Figure 2.3 Regulation 18 notices served versus those submitted to the Secretary of State
Reasons for serving notices
Most notices are historically served in response to a failure of a microbiological standard, with a small minority for failures of other standards. In 2024, 69 out of the 114 notices submitted were served for failures of microbiological standards.
The tenet of the Regulations is one of proactive risk assessment to prevent failures and a risk to health from ever being realised, and it is welcome to see that 11 were served due to actions from this process and one notice was put in place due to a lack of risk assessment.
However, local authorities still appear to be predominantly reacting to sample results, rather than proactively eliminating the problems that would result in a sample failure. The use of a proactive risk assessment, and if necessary, a notice in this context, is to protect users before an incident occurs so they are not unsuspecting, and they can be responsible for protecting their own health.
Table 2 Notices served
| Reason for serving the notice | Number |
| Risk assessment | 11 |
| Lack of risk assessment | 1 |
| Bacteria | 69 |
| Nitrate | 16 |
| Multiple parameters | 9 |
| Multiple metals | 1 |
| Arsenic | 3 |
| Fluoride | 2 |
| Manganese | 1 |
| Nitrate and nitrite | 1 |
| Total | 114 |
Sixty-nine notices were served for microbiological drivers. The majority of these required treatment systems to be serviced or the installation of additional treatment.
Three mentioned making changes to the source or source protection, which is worth considering for some supplies where changes in the catchment have been noted as part of the risk assessment and investigation following a sample failure.
Some notices mentioned the use of UV as a method of disinfecting the water. It is worth noting that where supplies are at risk of viral contamination, such as faecal contaminated supplies, UV disinfection may not be suitable when used alone and additional treatment for viral removal or inactivation may need to be considered through the risk assessment process.