Microbial risk assessment of drinking water to set health-based performance targets to improve water quality and treatment plant operations

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Western Water (WW) provides water, recycled water and wastewater services to almost 150,000 people whilst continuously striving to improve processes to provide its customers with safe, cost effective and reliable drinking water, recycled water and treatment services. Under this framework of continuous improvement, WW has reviewed the effectiveness of its drinking water treatment systems using quantitative microbial risk assessment (QMRA) techniques described by the World Health Organization (WHO). The microbial-related water quality targets in the Australian Drinking Water Guidelines Paper 6 National Water Quality Management Strategy (2011) National Health and Medical Research Council, National Resource Management Ministerial Council, Commonwealth of Australia, Canberra are simply ‘to ensure that drinking water is free of microorganisms that can cause disease’. Whereas, the Australian Guidelines for Water Recycling adopted the WHO QMRA approach for setting health-based microbial targets to manage health risk to customers. WW has investigated adopting the AGWR methodology for drinking water risk management, and invested in the development of a convenient and practical QMRA tool for rapid assessment and reporting of the microbial safety of its drinking water systems. This action resulted in the identification of several drinking water system performance deficiencies, and recommendations for system improvements and optimization to improve health risk management to customers.