In Search of Safe Drinking Water

Access to safe drinking water is a fundamental requirement for good health and is also a human right. WHO and UNICEF’s indicator is based upon the “use of an improved source”. The authors of a recent study into water contamination postulated that this did not account for water quality measurements or monitor global access to safe drinking water. Researchers Robert Bain and Jamie Bartram from The Water Institute at University of North Carolina sought to determine whether water from “improved” sources is less likely to contain fecal contamination than “unimproved” sources and to assess the extent to which contamination varies by source type and setting.

Studies from online databases published between 1990 and August 2013 in Chinese, English, French, Portuguese, and Spanish were identified, including PubMed and Web of Science, and grey literature. Using this data, the researchers investigated the risk factors and settings where fecal contamination of water sources was most common.

Studies in low and middle income countries that assessed drinking water for the presence of Escherichia coli or thermotolerant coliforms (TTC) were included provided they associated results with a particular source type. In total 319 studies were included, reporting on 96,737 water samples. The odds of contamination within a given study were considerably lower for “improved” sources than “unimproved” sources.

However over a quarter of samples from improved sources contained fecal contamination in 38% of 191 studies. Water sources in low-income countries and rural areas were more likely to be contaminated.  Thus, safety may be overestimated due to infrequent water sampling and deterioration in quality prior to consumption, having profound implications for public health policy.

These findings are important as WHO and UNICEF track progress towards the Millennium Development Goals water target using the indicator “use of an improved source”: this study shows that assuming that “improved” water sources are safe greatly overestimates the number of people thought to have access to water from a safe source, suggesting that a large proportion of the world’s population still use unsafe water.

Access to an “improved source”, such as piped water and bore holes provides a measure of sanitary protection but does not ensure water is free of fecal contamination nor is it consistent between source types or settings. International estimates therefore greatly overstate use of safe drinking water and do not fully reflect disparities in access. An enhanced monitoring strategy would combine indicators of sanitary protection with measures of water quality.

Read more from PLOS Medicine.

Article by Robin Blackstone.