Private Water Supplies - Case Study 2011/10

Consumer complaint of illness highlighting an inadequate approach to maintenance by the owner

This case study relates to a small supply serving 11 domestic dwellings, five of which are rented. The source is a borehole surrounded by pastureland grazed by domestic livestock (sheep) and the supply is disinfected with chlorine.

The local authority sampled from one of the properties after receiving a complaint from the tenant about the quality of the water due to illness among children in the household. The sample results showed that the water contained E.coli. The approach taken by the local authority was to advise all users to boil water before use or use bottled water, by putting in place a Regulation 18 Notice. They then prioritised the risk assessment for the site, which served as the investigation.

After all the consumers had been informed about the sample results, the tenant who had complained originally, made contact again to report a strong chlorine taste and odour. When the local authority arrived on site to investigate, the chlorine taste and odour had dissipated and the complaint could not be substantiated. However, during the risk assessment it was found that the chlorination system had malfunctioned and the owner of the supply was manually dosing chlorine on an ad-hoc basis. The owner stated that this was being done while awaiting attendance of the contractor to repair the system. This temporary measure had been going on for five weeks and although the contractor had been notified no action had been taken. The local authority added to the Notice the need for the disinfection system to be repaired along with other improvements.

The contractors repaired the chlorination system and also checked a UV system which served one property. Prior to revoking the Notice the local authority took a bacteriological sample, as well as a field chlorine test to verify that water quality was satisfactory and chlorine levels were in line with the doses expected from the repaired disinfection system, in case the owner of the supply had manually dosed it, prior to any microbiological sampling. On-site chlorine tests are recommended in the Microbiology of Drinking Water1 and are essential to calibrate dosing equipment and check it is operating within specification as detailed in the guidance on chlorine test method calibration on

Vegetation overgrowing reservoir

a. Vegetation overgrowing reservoir
b. Vegetation overgrowing reservoir

This case study illustrates the flexibility of Notices, which in this case included requirements for servicing and maintenance of equipment to prevent malfunctions. Details of contingency requirements can also be included, such as devices to ensure the supply is safe and effectively disinfected i.e. alarms, UV lamp efficacy or UV lamp-life indicators, turbidity and chlorine monitors. All equipment requires regular checks with the keeping of records. The Notice also required improvement at the source to prevent contamination from livestock and wildlife, including installation of watertight covers on the storage tanks and chambers, clearance of vegetation and soil from the reservoir cover, provision of a diversion ditch to prevent surface ingress into the source and collection chambers, and livestock and rabbit-proof fencing. The local authority used the risk assessment as the basis of its investigation. There was no appeal to the Notice and it was revoked once the works had been completed and a satisfactory sample verified that the control measures were effective (treatment, well managed and maintained system).

This case study illustrates the importance of adequate maintenance to the effective functioning of any treatment system in place, the absence of which renders the treatment virtually useless in terms of protecting public health. It also highlights the need, during risk assessment, to consider the knowledge and attitude of the owner/operator as a potential hazard. In this case the local authority identified a lack of procedures, by the owner of the supply, for communicating with consumers and keeping them informed about water quality and the safety of the supply.

1The Microbiology of Drinking Water (2010) – Part 2 – Practices and procedures for sampling. Available at -2-232.pdf