Microbiological surveillance of private water supplies in England – The impact of environmental and climate factors on water quality

• Published in: Water research (Oxford) Vol. 43; no. 8; pp. 2159 - 2168
• Main Authors: Richardson, Hopi Yip, Nichols, Gordon, Lane, Chris, Lake, Iain R., Hunter, Paul R.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-05-2009; Elsevier
• Subjects: Applied sciences; Cattle; Climate; climatic factors; drinking water; England; environmental monitoring; Escherichia coli; Escherichia coli - isolation & purification; Exact sciences and technology; Freshwater; groundwater; hydrologic models; microbial contamination; Monte Carlo method; Multivariate Analysis; Other industrial wastes. Sewage sludge; Pollution; private sector; probability analysis; Rainfall; Risk Assessment; Rural water supply; seasonal variation; Sheep; springs (water); surface water; Wastes; Water - standards; Water Microbiology; Water Pollution; water quality; water supply; Water Supply - standards; Water treatment and pollution; England; United Kingdom; Great Britain; Europe; British Isles, England; Climate; Cattle; Escherichia coli; Risk assessment; Rural water supply; Rainfall; Sheep; Drinking water; Monte Carlo method; Water supply; Environmental factor; Modeling; Confidence interval; Rain; Pollution; Surveillance; Environment impact; Surface water; Water quality; Rural area; Bacteria; Enterobacteriaceae; Ground water
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2009.02.035

A passive surveillance system captured information on 34,904 microbiological samples from 11,233 private drinking water supplies within England as well as the associated constructional, climatic and environmental variables.
Escherichia coli was detected in 6588 (18.87%) of samples and at least one positive sample was detected from 3638 (32.39%) of sites. However, this estimate of supplies failing to meet the European drinking water
E. coli standard was probably an underestimate as the more samples taken per supply, the more likely the supply was to fail. A multivariable model of private water supplies data showed a strong seasonal impact, with samples between January and May being significantly less contaminated with
E. coli than samples between June and December. Samples from springs (OR 2.5, CI 2.0–3.1) or surface waters (OR 2.4, CI 0.8–7.0) were more likely to fail than groundwater sources, as were supplies with no effective treatment (OR1.8, CI 1.5–2.3). Commercial supplies were less likely to fail than domestic supplies (OR 0.63, CI 0.48–0.83) and the probability of failure was linearly associated with the density of sheep in the area and rainfall on the previous day. A Monte Carlo modelling approach was used to estimate that, had sufficient samples been taken, 54% (95% confidence intervals 49–59%) of all private water supplies in England were likely to be unsatisfactory. These findings will be able to inform risk assessments of private water supplies prior to microbiological results being available.