AWWA PATH56517

One of the primary goals stated by the World Health Organization is that all people should have access to adequate amounts of safe drinking water. This goal is however far from being reached, especially in developing countries. Even in countries with highly developed water treatment major outbreaks occur. Sweden has a large supply of clean water but still experiences a few waterborne outbreaks every year. The most common causes of waterborne outbreaks are increased faecal contamination of source waters in combination with defect disinfection or intrusion of wastewater into distribution networks. Furthermore, inadequate treatment and distribution under "normal" operation may result in infections in consumers. Enhanced water security may be achieved by protection of source waters or the use of alternative water sources. Supplementary treatment barriers, such as ozone, UV, membranes etc., can also be applied. However, additional treatment at the water works does not reduce the risk from incidents involving the distribution network. If a barrier could be positioned just before the point of use, contamination during water distribution could be moderated. The potential of decentralized water treatment at the household block level, thus, needs further attention and are being investigated within the framework of the Sustainable Urban Water Management program in Sweden. Conventional water treatment and distribution was compared with two theoretical decentralized membrane alternatives in terms of resource use, environmental impacts and microbial risks. The objective of this paper was to expand the study of Westrell et al. to include the influence of failure or events, in treatment and distribution, on the annual risk of infection through drinking water consumption. Based on the rates of infection from the conventional system, the level of "tolerable" failures from decentralized membrane systems are discussed. Another question of concern is whether incidents or low-level background contamination during normal operation is the main contributor to the annual risk of infection. Microbial health risks were evaluated by means of quantitative microbial risk assessment (QMRA). Three pathogens were included, Cryptosporidium parvum, rotavirus and Campylobacter jejuni, all of which are waterborne pathogens of major health impact in Sweden as well as internationally. These microorganisms also serve as index organisms for the range of pathogens (bacteria, viruses and protozoa) in this study, since their behavior and resistance towards different treatments vary substantially. Includes 8 references, figure.