A survey of the microbiological quality of private water supplies in England

Results from statutory testing of private water supplies in nine Public Hea lth Laboratories in England were compiled, and the effects of supply class, source, treatment and location on water quality were examined. A total of 6551 samples from 2911 supplies was examined, over a 2-year period, of whic h 1342 (21 %) samples, and 949 (33 %) supplies on at least one occasion, fa iled current regulations for Escherichia roll. Total coliforms, including E . coli, were detected in 1751 (27 %) samples from 1215 (42 %) supplies. The percentage of samples positive for E. coli was highest in summer and autum n, and lowest in winter. Samples taken from larger supplies and fi om boreh oles were less frequently contaminated than those from other sources, Chlor ination, filtration or UV light treatment improved the bacteriological qual ity of supplies, but still resulted in a low level of compliance with the r egulations. The public health implications of the study are discussed.