N-nitrosodiumdimethylamine (NDMA) in drinking water is one of many factors – such as a persons’ genes – that cause cancer. Although NDMA is not a sole cause of cancer, the water industry aims to minimise its contribution to illness and disease. This research measured levels of NDMA in drinking and recycled waters and found the majority well below the Australian Drinking Water Guideline values that are considered safe for public consumption. Different sources of NDMA were identified and water monitoring and treatment strategies to optimise NDMA removal from source waters were recommended.

Disinfection is essential for removing harmful microbial pathogens and making safe drinking water but can also cause formation of disinfection by-products (DBPs), some of which pose a health risk. Thirty years of research have amassed a wealth of knowledge about the identification, formation, treatment and control, toxicology and epidemiology of DBPs in Australia. This project compiled, assessed and presented an overview of DBP-related research in Australia.

Microscopic pathogens in drinking water pose a risk to public health. In Australia, chlorine or chloramine are used to inactivate these pathogens, to disinfect drinking water and prevent widespread outbreaks of debilitating illness in large populations. Although largely successful, problems arise when drinking water is contaminated by pathogens after being disinfected in the treatment plant but before reaching the customer. A variety of situations cause this, one being small pipe leaks which become a route for soil micro-organisms to get into drinking water. To prevent pathogen contamination in pipe networks, higher levels of disinfectants can be added at the treatment plant, or secondary disinfection can be administered in the pipe network. This research project produced a guidance manual which explains how to maintain and monitor effective disinfection levels in post-treatment pipelines, and the major challenges to maintaining effective disinfection.

Chlorine removes harmful pathogens from water but has the disadvantage of forming disinfection by-products (DBPs) by reacting with organic matter sometimes found in water. Chloramine also disinfects, is less likely to form DBPs and is more stable, so remains active in for longer in the pipelines which distribute drinking water from the plant to the tap. The problem is that it is difficult to predict exactly how much chloramine to add; it needs to be enough to maintain disinfecting activity in the pipeline distribution system, but not so much that customers find the smell of chlorine in tap water unpleasant. Traditionally, the chemical reaction rate has been used to predict the gradual ‘decay’ of chloramine in pipelines, but this is inaccurate. This research developed a computer software statistical programme that uses ‘artificial neural network’ concepts and operations to predict the longevity of chloramine residuals in water distribution systems. This is more accurate than traditional methods.

Cyanobacterial blooms are a major problem for reservoir managers because of the large numbers of cells and the toxins they contain. These blue-green algae blooms have traditionally been treated with the algaecide copper sulphate, but this was expensive and unsustainable because it killed non-target species and left residual contaminants. This research examined and rejected alternatives: other copper-based algaecides, hydrogen peroxide, substances that trap cyanobacterial-growth supporting nutrients on the floor of the reservoir, and mechanical surface mixers. Laboratory experiments that tested the ability of ultrasound to prevent the photosynthetic cyanobacteria from floating at the depth that optimises light absorption were initially promising because the ultrasound reduced photosynthesis and metabolism and the blue-green algae died. Unfortunately, when an ultrasound system was deployed in a reservoir, the much larger volume of water attenuated and ‘absorbed’ the low-power ultrasound and led to the conclusion that sustainable, environmentally friendly levels of ultrasound do not provide effective control of blue-green algae. This rigorously conducted scientific study has generated useful information about methods which do not work, and resources can now be directed to promising new innovations.

Water is disinfected to remove harmful organisms, then filtered and treated to remove contaminating pollutants. The treated water then enters distribution pipe networks which eventually terminate at customers taps. The distribution systems can be many kilometres long and if the drinking water is in the distribution system for extended periods of time, the activity of the disinfectant gradually declines. This project used a laboratory model of a representative distribution system to make changes to initial water treatment, then examined their effects on the maintenance of disinfection and water quality.

This paper discusses various water quality risk management techniques and proposes a step-by-step catchment risk assessment methodology that is compatible with the Australian Drinking Water Guidelines.