Report No DWI0774
Health Risks from Private Water Supplies
Under the Private Water Supplies Regulations 1991, which came into force on
January 1 1992, local authorities are required to monitor the quality of such supplies in their areas. Although it has been estimated that less than 1% of the population receive their drinking water from private supplies, a larger number of people are, often unknowingly, exposed to such supplies through their use in hospitals, hotels and campsites and in food production.
This study, which was funded by the Department of the Environment and managed by the Drinking Water Inspectorate, was undertaken with the following objectives:
Twice weekly water samples were taken from 91 private supplies, in ten local authority areas, over a six week period. These 1100 samples were analysed for total coliforms, faecal coliforms and faecal streptococci.
The microbiological quality of the private water supplies examined in this survey is generally poor, with almost 50% of the supplies examined failing to meet the required standards on at least one occasion.
The most common reason for failure was the presence of total coliforms (15% of samples), followed by faecal streptococci (12.7%) and faecal coliforms (9%).
While the majority of the private water supplies examined in this survey received no form of treatment, use of W or chlorination was not a guarantee of sample compliance.
Very few reports of outbreaks of infectious illness attributable to the consumption of private water supplies have been published. However, details of 18 outbreaks affecting over 2,000 people were identified. The most commonly reported illness was campylobacter enteritis.
Given the constraints of this study it is not possible to determine whether or not there is a significant health risk from the consumption of private water supplies. However, given the high level of microbiological failures there is the possibility that harmful microorganisms could be present and a significant risk to health cannot be discounted.
There was general concordance between this intensive monitoring data and the local authority information. Faecal streptococci concentration is, however, not measured by any of the local authorities surveyed. This indicator was found in 5% of the samples analysed during the present study in the absence of total and faecal coliforms. Inclusion of faecal streptococci enumeration may, therefore, provide useful additional information on water quality. Given the often intermittent nature of contamination, water quality will rarely be characterised by a single sample. However, there is now at least three years data for most supplies and a more complete picture is beginning to emerge.
Given the considerable variability in microbiological quality, it is recommended that the current regulatory monitoring requirements be reviewed.
Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.