Cryptosporidium, a microscopic pathogen, forms infectious oocysts which are removed by specific and targeted water treatments. Oocysts can only be seen by using a microscope but finding an infectious dose of 10 oocysts in a litre of water is like finding a needle in a haystack. Usually a larger volume of water, 1000mL, is filtered to recover all the oocysts into a small volume of 0.1 to 1 mL, because this is small enough to be examined under a microscope. It is scientific practice to add some dead, colour-dyed oocysts to the large volume of water. If all the coloured oocysts are counted on the filter, the recovery is 100%. From this it became clear that there was a problem with oocyst recovery. This research found that different elements reduced recovery from different types of water, for example, iron and silica reduced oocyst recovery from river or groundwaters. The approved method for quantifying the environmental occurrence of oocysts can now be modified to increase recovery, and this change improves analysis and consequent management which further reduces risks to public health.

Source waters are disinfected to remove harmful pathogens, but chlorine reacts with organic matter and bromides to form disinfection by-products (DBPs) which can affect health. Water treatment reduces DBPs to safe levels by using alum to remove organic matter before disinfection but some water sources, particularly those with high bromine levels, are still difficult to treat. This research aimed to compile the best protocols for alum coagulation and disinfection when source waters contain different levels of organic matter and bromides, and to relate these to health risks. When organic matter was removed with 125 mg/L alum, and this treated source water was disinfected twice, and the first dose was calculated to generate chlorine levels of 0.5 mg / L for two days before administering the second dose, then DBP levels in drinking water were minimised. Neither alum-treated nor disinfected water caused toxicity in two laboratory tests used to examine risks to health.

It is prohibitively expensive and time-consuming to monitor drinking water by individually quantifying every possible polluting contaminant. Instead, living cells can be cultured in samples of the test water and if one or more toxic contaminants are present the cells die. Less toxic, more subtle effects can also be measured, for example, a toxicity test that uses cells collected (decades ago) from one monkey kidney, quantifies cell death but also measures the amount of protein made by each live monkey kidney cell. The problem with this, and other toxicity tests, is that chlorine disinfectants and harmless low levels of other substances, such as aluminium or copper, which occur naturally in water, can sometimes have inhibitory effects on the ‘bare’ cells that are often more sensitive when cultured inside laboratory culture vessels than when they were in a normal situation within a body. This research identified commonly used toxicity tests that are not affected by disinfectants or naturally occurring harmless substances, and also worked out some solutions that quench disinfectants and allow cost-effective and useful cell-based toxicity tests to be used to monitor the safety and quality of drinking water.

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.