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.

Water treatment plants (WTP) take in source waters then remove 95-99% of blue-green algae (cyanobacteria) cells and the toxins they produce. During this removal process waste sludge is generated and transferred from clarifier tanks in the treatment plant to lagoons. It was thought that confinement in the sludge killed the cyanobacteria, but this research found that when algal blooms have generated very high cell numbers, viable, toxin-producing cyanobacteria are retained in the sludge and can release toxins into the clarifier supernatant. It was concluded that timely removal to lagoons will avoid problems, and it is recommended that risk assessment for recycling lagoon supernatant back to the head of the WTP should incorporate extended times of 3 to 4 weeks after the end of algal blooms, to ensure cyanobacterial cell death and toxin degradation.

This research was prompted by concerns that rooftop-harvested rainwater fed into household hot water services might expose the public to harmful pathogens such as salmonella. Householders can be exposed to untreated heated rainwater while washing and when this water is used to wash or prepare food. Water heated to 60°C and maintained at this temperature for several minutes’ kills most, but not all infectious pathogens. The problem is that many Australian hot water services operate at lower temperatures that do not kill enteric pathogens. In this study fewer than 5% of water samples collected from unheated rainwater tanks contained pathogens, but this relatively low frequency still poses a risk and is part of the reason that heated rainwater systems fail to meet existing guidelines for safety. Modifications that would improve safety include installing a device that prevents water cooler than 60°C leaving the storage tank and using cold potable water instead of cold rainwater for tempering or in mixer taps. UV disinfection devices attached to rainwater systems are an effective way to reduce health hazards to acceptable levels.

Cyanobacterial blooms in surface waters are a source of cells, taste and odour compounds, and a range of toxins. This research optimised treatment processes for the removal and control of cyanobacteria and their metabolites from a range of source waters. It was concluded that pre-chlorination is not advisable when cyanobacteria are present, but that in some situation’s potassium permanganate is a viable alternative. Although all three tested coagulants; ferric chloride, aluminium chlorohydrate and aluminium sulphate (alum) removed 90 to 95% of cells, alum at pH 6.3 was the most cost-effective. Maintaining pH > 6 reduced cell lysis and metabolite release. Since cyanobacteria in sludge remained viable for 2-3 weeks it was recommended that sludge detention in the clarifiers should be minimised.

Approximately 11% of Australians use rainwater as their main source of potable water but this poses a potential health risk caused by chemical contaminants or microbial pathogens from birds or mammals being washed off the roof. In this study, rainwater samples from 300 households in Adelaide were collected for over a year. There are so many factors affecting a persons’ health that it is not possible to directly correlate water quality to participants health, but there was no significant effect of rainwater on the incidence of gastroenteritis. Levels of lead were higher than recommended by the Australian Drinking Water Guidelines in 2% of the tanks, and bacterial load was higher after rain washed roofs and gutters clean. This led to the recommendation that First Flush devices should be installed to divert early rainfall waters away from storage tanks. Microbial pathogens that cause human gastroenteritis were not detected.