There are four main characteristics of drinking water used to describe its quality. These are: physical; microbiological; chemical; and radiological (page 1). Each of these four areas are very important in their own right. However, in Sydney, lately specific attention has been paid to the microbiological characteristics of drinking water (pages 8-15).

The protozoan parasites Cryptosporidium and Giardia have recently been detected in the distribution system of Sydney Water, leading to boil water alerts in the community (pages 17-24). The ingestion of the cysts of these organisms, which is the environmentally resistant stage of the pathogen, can result in diarrhoea and stomach cramps in affected persons. There is no treatment available for disease caught from Cryptosporidium, the body naturally repels the parasites after a period of time. However, in the immuno-suppressed, the body is less able to do this and death may result (pages 9-14).

Current drinking water guidelines in Australia provide little assistance for water supply authorities in relation to the presence of Cryptosporidium or Giardia in drinking water. Developments overseas, notably the United Kingdom and the United States, have provided some guidelines on international best practice for the presence of these pathogenic organisms in drinking water (pages 27-33).

Outbreaks of disease resulting from Cryptosporidium and Giardia contaminated drinking water have occurred around the world. In Milwaukee in the United States, a contamination event in 1993 resulted in over 400,000 people sick and 104 people died. In Sydney, while these organisms have recently been detected in the water distribution system, no increase in disease has been identified.

Modern water treatment plants like Prospect Treatment Plant should be able to remove 99% of Cryptosporidium oocysts. However, the Sydney Water Inquiry has concluded that this does not appear to be the case, and further disinfection technologies may need to be investigated for the Sydney water supply (pages 19-24). The source of the pathogenic organisms in the Sydney water supply is yet to be finally determined. Overseas, with similar outbreaks it has proved impossible to pinpoint the source of water contamination. In Sydney, considerable work can be done to improve the catchment management of Warragamba Dam, helping to eliminate some potential sources of contamination for the city's water supply (page 33).