Private Water Supplies - Case Study 2012/6

Repetition of illness among seasonal workers at a fruit farm associated with mismanagement of the domestic and non-domestic water supply arrangements on the premises

This case study relates to the water supply arrangements on a 200 acre fruit farm in England. There is a mains water supply to the premises, but there is also an irrigation system that can draw water from two other sources; a borehole and a river running alongside the boundary of the premises. During the fruit picking season approximately 160 seasonal workers are housed in static caravans on the site. In June 1992, there was a serious outbreak of waterborne disease (mainly campylobacter infections) among workers on this fruit farm and the investigation of the outbreak led to the previous site owners being prosecuted by the water company for failing to comply with the fittings regulations (specifically an open cross connection between the river water irrigation system and the mains water system). In May 2012, the site manager contacted the water company because once again there was illness among the seasonal workers residing on site and, for a period of four days, the water supply on the farm had been discoloured, with no similar problems being reported by neighbouring premises.

Samples collected the next day by the water company were visibly discoloured and turbid, containing particulate matter, but no measurable residual chlorine. These samples contained greater than 200 E.coli and Enterococci per 100ml and the total viable counts (heterotrophic plate count) were greater than 300 per ml. Further analysis of the samples identified the presence of algal species, typical of those found in river water generally, but also found in river samples. Shortly after the water company’s visit to the farm there was an unexplained resolution of the water discolouration problems on the farm and all subsequent follow-up samples gave satisfactory results. Nonetheless, the water company persisted with its investigations, which included the use of CCTV, and extended to the whole of the water supply network on the fruit farm, not just the part identified by the site owner as being problematic. Although a functional cross connection was not found during this site survey, evidence strongly suggestive of this as the cause was found in the form of a disconnected T piece at a point on the system where the mains supply and the irrigation system run in close proximity (see Figure 11).

Figure 11: Disconnected T piece

Figure 11: Disconnected T piece

The water company installed a new non-return valve on the inlet to the farm and, while the investigation was underway, made alternate bottled water supplies available in support of the ‘do not drink’ advice agreed with local health professionals.

This case illustrates the inherent high risk associated with sites where both non-domestic water systems and a mains supply are installed. The Inspectorate, water companies and local authorities to anticipate contamination events at periods of seasonal high demand for water on similar agricultural or horticultural premises. Such events may be caused accidentally (lack of knowledge) or deliberately (misuse), but in either case, timely, proactive and preventative site visits are recommended in the interests of public health.