Melbourne Water is the bulk water supplier for the City of Melbourne, Australia. Muchof the city's drinking water supply is drawn from protected, uninhabited catchmentsand delivered to consumers disinfected but unfiltered.After many years of drought, severe storms in catchment areas in mid-2007 resultedin a water quality incident with high raw water turbidity levels from wash-off intoreservoirs. A boil water notice was issued for small townships that received drinkingwater directly from the affected reservoir (Upper Yarra Reservoir).Melbourne Water has a certified risk management plan for drinking water quality(HACCP, ISO 9001, ISO14001) that requires research to be undertaken in areas ofthe water supply where risks are not fully understood or identified. Several years ofresearch into the presence of Cryptosporidium in catchment animals, combined withdetailed risk assessments and event-based sampling in catchment areas has shownthat the risk of contamination of the water supply with human-infectiousCryptosporidium is low.Research results, combined with a quantitative microbial risk assessment and resultsof genotyping of Cryptosporidium in water samples during the incident was presentedto the Victorian Department of Human Services, who determined that the risk ofhuman infectious Cryptosporidium to the consumers of Melbourne's drinking waterwas acceptable. As a result, a boil water notice for Melbourne was not issued. Thisexperience highlighted the importance of rigorous risk assessment and research tosupport water supply management decisions. Includes 7 references, tables, figures.
