The ADWG explains policies but does not provide the specific steps and actions needed to apply risk management principles within a water treatment plant (WTP). The original ‘Guide to Drinking Water Supply Systems for the Management of Microbial Risk’ (WaterRA Project 1074) filled this gap by providing Australian-specific advice about managing and optimising common water treatment processes to achieve microbial health-based targets. Since its publication in 2015 it has become a popular reference document, and its widespread acceptance and use has prompted the production of this second edition. Included are updated technologies and regulations, and a series of auditing tools and templates for application in a variety of situations, including the identification and quantification of risk.

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Microbial pathogens are removed from source waters to make safe drinking water. Health-based targets (HBTs) refer to the quantities of pathogens that will NOT cause illness, and water treatment plants (WTPs) must ensure that the numbers of pathogens in potable water are the same or lower than the HBTs. WTP operators select the best pathogen removal treatment for a range of conditions such as season, rainfall and agricultural activity by referring to ‘sanitary surveys’. These are carried out approximately once a year by scientists driving and walking in the source water catchment, making observations, and collecting samples which are examined to look for indicators of harmful pathogens. Recent requirements to achieve HBTs, combined with technological advances, led to this project which aims to provide flexible sanitary survey guidance applicable to the broad range of Australian conditions and utilities. This Good Practice Guide reviews existing procedures, describes modern methods including aerial photography and the use of spatial databases, and describes the incorporation of sanitary surveys into ongoing source water operational monitoring in ways that support the establishment of log removal values and enable compliance with HBTs.

The ADWG prioritises the removal of microscopic pathogens (and the toxins some produce) from public drinking water supplies to prevent large scale outbreaks of illness. This principle underlies the importance of adhering to consistently high standards of water treatment plant (WTP) operation and maintenance. This Guide refers primarily to the conventional WTP processes of chemical pre-treatment, coagulation, flocculation, clarification, filtration and disinfection; and establishes target criteria and critical limits for each step in the treatment process. The Guide is designed to provide water utility managers and operations staff with a concise reference document to optimising the WTP processes that produce microbially-safe drinking water and additionally supports the establishment of microbial Health-based targets.

The ADWG 2011 lacked objective, quantifiable criteria for measuring pathogen removal from source waters. The WHO requires that health-based targets (HBTs) are used to ensure safe drinking water. HBTs can be set by making ‘Disability Adjusted Life Year’ (DALY) calculations which incorporate information about a population; the average Australian lifespan and the impact of infection on the length of a healthy life. Pathogen levels in water that correspond to micro-DALYs with minimal population-level effects are too low to be detectable by existing tests. This problem is addressed by calculating ‘log removal values’ (LRVs). Pathogens can be measured in source and treated water after the application of a defined method. When 90% of the pathogen is removed, the LRV equals 1, while 99% removal has an LRV of 2. HBTs incorporate LRVs, which are based on objective, quantifiable criteria, to reduce pathogen loads to levels that correspond to acceptable Australian micro-DALY levels. This research collated existing datasets about pathogens in source waters and the efficiency of their removal by treatment plants around Australia. From this, default pathogen levels for a range of Australian source waters and climate events, and LRVs for different treatment methodologies were obtained.