Deficiencies in proactive risk assessment on a regulation 9 supply
Background
In April 2024 the Inspectorate was invited to discuss water quality issues at a regulation 9 private water supply with members of the local authority, the UK Health Security Agency (UKHSA), and the local water company.
In a residential area of the West Midlands, a complex of interwar apartments was being served by an on-site borehole, providing water for domestic purposes to 300 consumers. The supply was controlled by a property management company, which utilised contractors to operate and maintain the borehole and subsequent treatment.
Statutory regulation 9 sampling by the local authority highlighted a rising trend in arsenic levels. When test results were over the maximum concentration stipulated in the Regulations, the site would often be temporarily switched over to a back-up mains water supply.
Investigation
The local authority contacted both the UKHSA and the local water company, Severn Trent Water, for advice. The UKHSA conducted their own health-focused risk assessment. Severn Trent Water elected to conduct investigatory sampling on behalf of the local authority across the site as well as at the borehole. Analysis at consumer taps found arsenic at similar concentrations to the untreated borehole water. It was suspected that the treatment of the borehole supply was ineffective, in part due to the blinding of the filtration system. The water company advised on potential improvements to the water treatment system on-site, if the borehole was to be used as a private supply going forwards. Otherwise, the site was in the advantageous position in that a direct switch to a mains water supply was feasible, an option which many private water supplies do not have.
Over the previous two years the complex had been temporarily switched from the borehole supply to the mains water supply on at least two occasions, as required by a regulation 18 notice from the local authority. This switch would take place following test failures; the filters would then be serviced, and the borehole supply would be brought back into use following a passing re-test. However, it is not sufficient to only resample at the point of contravention to ‘confirm’ a sample result. The purpose of an investigation (as required by regulation 16) is to determine the cause of the water being unwholesome which will establish the necessary actions to ensure that the advice given to the relevant person will protect consumers in the long term. The evidence showed that the on-site treatment could not secure wholesome water that was not a risk to health continuously, and for the long term. Therefore, this should have resulted in a regulation 18 notice securing a permanent and long-term control measure, rather than a temporary switch to the public supply, while inadequate maintenance was delivered on an ineffective treatment process.
Solution
The site is now permanently on a mains water supply. Analysis at consumers taps, particularly at the extremities of the supply system showed that high-arsenic water remained in the system for longer than anticipated, extending to more than three weeks. This latency was attributed to dead legs in the private system, low turnover, and the presence of large cold-water storage tanks for the bathrooms. This meant that when arsenic concentrations within the supply were high, the duration from the point in time this occurred, to the point the high-arsenic water in the system was fully replaced with safe mains water in reaction to the local authority’s programmed sample, could have been many months.
Private water supply practitioners are reminded that understanding the network, its size, volume, and turnover is fundamental in the effective management of a private supply, protecting public health and informing a suitable risk assessment and risk management strategy. Notices should be used to secure long term solutions to water quality issues that are a risk to health.