Private Water Supplies - Case Study

Investigation following a breach of the lead standard on a regulation 9 private water supply


The detection of lead at any concentration from a private water supply used for human consumption is a cause for concern. Any lead concentrations found above the regulatory standard of 10 µg/L must be regarded as a potential danger to human health. The local authority must investigate and serve a notice in accordance with the relevant parts of the regulations1 where these circumstances are applicable.  

The risk of this is greater in premises constructed before 1970 when lead was banned as a material for use in drinking water pipes.  Most commonly, the cause of lead in private water supplies is due to plumbosolvency (lead dissolving). Where there are lead pipes and or other lead fittings in the water distribution system within premises these may deteriorate over time. Solder which has been used on plumbing that is wholly or partly made of lead is also a common source. Other causes may include source contaminants from disused lead mines and other catchment pollution sources such as land fill sites. 

Lead in private supplies may also arise from some metal fittings that are situated between the supply source and the point at which the domestic distribution system begins.  

Prior to the implementation of risk based private water supply regulation in 2010 the occurrence of lead on a supply system was more likely to have gone undetected, as this case study will illustrate. 

Supply and sample details 

In November 2022 the Inspectorate received an enquiry from a local authority reporting a higher-than-expected lead result from a random daytime (pre-flush) sample taken from a large (regulation 9) private supply in a property that was occupied by tenants under a rental agreement. The result of 55.8 µg/L was well above the regulatory standard of 10 µg/L.  

Up until the time that this sample was taken, neither the twice-yearly monitoring of this supply, or its five yearly risk assessment review had highlighted any risk posed by the presence of lead in the water.  

Regulatory sampling was being rotated around the houses on the supply, and this was the first time that a sample had been taken from this particular property. In response, the local authority informed the house owner of the result and advised that they “ran the tap for a few minutes” prior to drinking it or alternatively to use bottled water for this purpose instead.  

The owner and occupiers of the house had been consuming the water for over 50 years. They believed that the service pipe to their home was made of lead, but they had never given any consideration to the risk this posed to their health over this duration. The local authority believed that the distribution network linking the properties to the supply source was not made of lead but instead was made of cast iron.  

The local authority sought clarification on what additional next steps they were duty bound to take. This included advice on whether they were required to serve a notice or not, on the basis that the cause was assumed to be the distribution system within the domestic premises.  

Local authority investigation 

The Inspectorate confirmed that thus far, the local authority had acted appropriately and in accordance with regulation 15 (17 in Wales) (provision of information). This requires them to inform and protect people that are likely to consume the water where it is a potential danger to human health. However, they were advised to ensure that the restriction-of-use be extended to the cleaning of teeth, not just for drinking. This is because the scope of the regulations, which covers “water intended for human consumption” includes other domestic purposes, such as cooking, food preparation and sanitary purposes, as well as for drinking. 

The inspectorate informed the local authority that further steps were necessary under regulation 16 (18 in Wales) to investigate and establish/prove the cause of the unwholesome water, as it was only speculative at this stage. As part of their investigation, the local authority was advised to visually inspect any pipework as best as they could, and to carry out additional sampling across the supply, to include pre-flush samples and a 30 minute stagnation sample from the property from where the breached sample was taken. The main purpose of this was to establish the extent of any risk to consumers and to confirm (or not) the suspected cause. The outcome of this would inform the next steps.  

The local authority’s subsequent investigation isolated the source of the lead to the service pipe on the property. Flushing the tap for 10 minutes reduced the concentration of lead to below the regulatory standard of 10 µg/L. A further lead result of 5.4 µg/L was also detected in a random pre-flush daytime sample from another property on the supply, whilst samples from other properties were lead free. 

Establishing whether the cause is associated with the distribution system within a domestic premises is important as not all circumstances require the local authority to serve a notice.  

Unfortunately, the Regulations do not define where on a private water supply the domestic distribution systems starts and ends. As a general guide, the domestic distribution system on a public supply comprises the water plumbing system within a dwelling, along with the service pipe up to the point where it joins the water company owned pipe, which is known as the communication pipe.  

Public health implications 

The United Kingdom Health Security Agency (UKHSA) advised the local authority that whilst concentrations were below the standard of 10 µg/L, there is no safe concentration in drinking water. Exposure to lead should be kept as low as reasonably practicable. UKHSA recommend that all individuals do not drink or cook with drinking water containing lead above 10 µg/L on a regular or long-term basis. 

The local authority passed on the UKHSA’s written advisory note on lead to the occupiers of the affected property. The Inspectorate later suggested that this advice also be provided to the second property where elevated lead levels had been detected, even though it was below the standard.  

This was in keeping with the UKHSA’s flushing advice to keep any exposure to lead as low as possible. This met the requirement of regulation 16(2) (18(2) in Wales) that local authorities, under all circumstances, must promptly inform the people likely to be affected and offer them advice on measures necessary for the protection of public health. The Inspectorate also suggested that it would be prudent for the local authority to further investigate the cause and risk of lead at this second property where lead had been detected. 

Local authority actions 

Regulation 16 (18 in Wales) (Investigations) requires local authorities to serve a notice where the cause of the water being unwholesome is due to the distribution system within a domestic premises (a) where the water is made available to the public or (b) the cause is NOT due to the distribution system within domestic premises (in other words, any other circumstance).  

The local authority concluded from their investigation that neither (a) or (b) were applicable, and that the responsibility for mitigating the risk was the owner/occupier of the property. The local authority advised that the owner/occupiers of the affected dwelling that they instruct a contractor to check the integrity of the service pipe and replace any lead pipe or fitting where it was found.  

Whilst updating the Inspectorate, the local authority requested confirmation that they had acted appropriately and in accordance with the necessary regulatory requirements, which it had. The Inspectorate confirmed that no further actions were required, but it should keep a record of its investigation as part of its regulation 6 risk assessment records. 

Local authorities have no specific duty to enforce the replacement of lead pipes where the cause is the distribution system in domestic premises, where the circumstances in regulations 16(5), (18)(5) in Wales do not apply. Neither are the property owners compelled by regulations to inform subsequent occupiers of any associated risk where it is not done.  The local authority should however establish any change of ownership as part of its five yearly regulation 6 risk assessment review, and inform and advise any new owners/occupiers, as per regulation 15 (17 in Wales).  

Conclusions and learning 

The local authority acted appropriately, seeking advice from both the UKHSA and the Inspectorate to help inform its investigation and direct its actions to protect consumers. This case demonstrates the sequence of steps that local authorities must take in the event of unwholesome water being established when water is suspected or confirmed as being unwholesome. In this instance this was due to lead sample results that were above the regulatory standard, which presents a potential danger to human health. 

This case study shows that the cause, once established by an investigation, will determine whether it is necessary for a local authority to serve a notice. In this case, whilst the risk presented a potential danger to human health, the circumstances described in paragraph 5 of regulation 16 were not applicable, so a notice was not required. The local authority was however obliged to inform the people likely to be affected and offer them advice on necessary measures for the protection of human health, which they did.  This must be done in all cases, irrespective of the circumstances. 

This case study also shows that when lead service pipes on a domestic premise are found to be the cause, other premises on the same supply may also share the same risk, particularly when they were built around the same time. This illustrates why investigations should be wider than simply resampling at the point of the original contravention.  

Investigations should include site checks to establish if any changes have taken place since the last supply risk assessment, and to determine the cause of a specific parameter breach. Where lead is detected for example, a simple inspection of the pipe running to the tap below the sink may reveal that is made of lead. Any shiny silver metal that is revealed by gently scraping away the dark outer surface of a pipe that is clearly not plastic or copper is indicative that it may be made of lead. Pre-flush sampling and samples taken at timed intervals following flushing are also helpful in conducting regulation 16 (18 in Wales) investigations following the detection of lead in a private water supply. 

It should be noted that a tenancy agreement at a domestic premises does not constitute an example of where water is being made available to the public. Such arrangements where this is the case however, include: a house that offers beverages to the public as a commercial enterprise, (for example, in a room of a dwelling designated and licenced for such purposes), any other public building where an owner occupier lives on the premises, any dwelling where charitable events are held (for example, coffee mornings to raise funding), and any owner occupied private estate where temporary festivals, fairs are held on its lands (for example, a privately owned and occupied stately home).