How can a private water supply affect health? Literature review 2008

Mains water vs Private Water Supply

The quality of drinking water supplied to those people on the mains in the United Kingdom is regularly analysed to make sure that it meets the standards set by the European Commission. The responsibility for independently monitoring the water companies rests with the Drinking Water Inspectorate (DWI) and they advise the government of their performance. According to the report submitted by the Chief Inspector of the Drinking Water Inspectorate (DWI, 2005), English water companies carried out just over 1.8 million tests and the mean compliance rate was 99.94%. On a local level, Yorkshire Water carried out 447,822 tests with a compliance rate of 99.97%. The DWI (2005) report these statistics as showing that the water provided by this company is generally of a very high quality and the health risks relating to drinking mains water remains low. However,  Medema et al. (2003) believes the microbiological quality of water should remain a cause of concern for all water suppliers, regulators and public health authorities as the potential for drinking water to transport microbial pathogens to great numbers of people causing subsequent illness, is well documented in all countries at all levels of economic development.

Untreated water from a private water supply can be harmful to health

Private water supplies are not regulated by the Drinking Water Inspectorate, but are the responsibility of local authority environmental health departments who must register the supplies and approve them based on a regime of chemical and microbiological analysis of water samples (Smith et al., 2006).

The report on the outbreaks of waterborne infectious intestinal disease in England and Wales (Smith et al., 2006) reports 89 outbreaks of waterborne diseases affecting 4321 people in England and Wales for the period 1992 to 2003. Public water supplies were implicated in 24 outbreaks (27%); private water supplies in 25 (28%); swimming pools in 35 (39%) and other sources in five outbreaks (6%). There are 56 potentially pathogenic organisms that can be found in drinking-water (Clapham, 2004) with the majority of waterborne outbreaks in private water supplies caused by CampylobacterE.coli 0157, Cryptosporidium and Giardia (PWS Technical Manual, 2007). Supporting this view, Said et al. (2003) identified the pathogens infecting private water supplies in the period 1970 to 2000, based on 25 reported outbreaks, as being Campylobacter 13 (52%), Cryptosporidium and Giardia 4 (16%), Cryptosporidium and Campylobacter 2 (8%), E.coli 0157 1 (4%). No pathogens were identified in 4 (16%) despite microbiological investigation. One of the outbreaks (4%) implicated Giardia and/or Campylobacter, but no actual causation agent was identified. Other pathogens of potential concern are Streptobacillus, Enteric viruses and Paratyphoid, however, these pathogens are rarely found in United Kingdom private water supplies (DWI, 2001).

Illness from a private water supply is 35% higher than from mains

The report on outbreaks of infectious disease associated with private drinking water supplies in England and Wales for the period 1970 to 2000 (Said et al., 2003) reports the incidence rate of outbreaks for recipients of private water supplies may be as high as 35 times the rate of those receiving public water supplies. The figure of 35 was based on 53 outbreaks per million population on mains supplies compared to 1830 outbreaks per million population for private water supplies. Clapham (2008) believes the figure for outbreaks for private water supplies is closer to 50 times higher than that of a mains supply if only the figures for the last 10 years are considered.

The most common symptoms

The Said et al. (2003) report highlights 25 outbreaks with private water supplies and subsequent investigations identified 1584 cases and at least 5190 people at risk. The most common symptoms were gastrointestinal and there were no recorded secondary cases of death, although there were several hospital admissions. Clapham (2004) believes these figures underestimate the true number of outbreaks for private water supplies because of general under-reporting of gastrointestinal illness. Supporting evidence for this view is contained in a paper by Wheeler et al. (1999) which concluded that for every case of infectious intestinal disease identified by the national surveillance system, another 1.4 were identified by laboratories. This study concluded that infectious intestinal disease is common, with 9.4 million estimated cases each year in England. However, only 1.5 million were presented to a general practitioner and only a fraction of cases involving Campylobacter being reported to national surveillance.

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