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Contaminants from the soil surrounding drinking water distribution systems are thought to not enter the drinking water when sufficient internal pressure is maintained. Pressure transients may cause short intervals of negative pressure, and the soil near drinking water pipes often contains fecal material due to the proximity of sewage lines, so that a pressure event may cause intrusion of pathogens. This paper presents a risk model for predicting intrusion and dilution of viruses and their transport to consumers. Random entry and dilution of virus was simulated by embedding the hydraulic model into a Monte Carlo simulation. Special attention was given to adjusting for the coincidence of virus presence and use of tap water, as independently occurring short-term events within the longer interval that the virus is predicted to travel in any branch of the distribution system. The probability that a consumer drinks water contaminated with virus is small, but when this happens the virus concentration tends to be high and the risk of infection may be considerable. The spatial distribution of infection risk is highly heterogeneous. The presence of a chlorine residual reduces the infection risk. [ABSTRACT FROM AUTHOR]

A retrospective analysis of coliform events in a drinking water distribution system was conducted. A total of 13 coliform isolates with specific geographic/sampling records were analysed using microbial source tracking (MST) to establish genetic (based on DNA) and phenotypic (based on substrate utilization) relatedness between isolates, and a data integration approach (geo-spatial and event analysis) to identify potential causes for their presence. Phenotypic analysis, using the APIw 20E system, identified two major genera: Enterobacter and Citrobacter, showing a high degree of phenotypic similarity within each species. However genotypic analysis (using pulsed field gel electrophoresis) of the Enterobacter and Citrobacter isolates demonstrated a wide genetic diversity within each species. The data integration approach revealed the probable causes for coliform events were the installation of new mains (8 samples) and rehabilitation of existing main (1 sample). The data integration and MST approach (genotyping) suggested that these coliform events were a result of sporadic intrusion from maintenance events and not chronic biofilm re-growth. The combination of MST and the data integration approach offers utilities a potentially powerful tool for the examination and determination of coliform occurrences in a distribution system. [ABSTRACT FROM AUTHOR]