CSIRO (Commonwealth Scientific and Industrial Research Organization) has for some years carried out research into more efficient ways of purifying water and wastewater. More intensive processing has been achieved by the use of finely divided solid reagents which can be regenerated and reused. The age-old problem of quickly separating the very small particles of loaded reagent from the accompanying liquid has been solved by utilizing a magnetic reagent in the form of magnetite, Fe3O4. A water clarification process is fully developed for the production of potable supplies from low quality ground and surface waters, with five plants in operation or under construction in Australia, the United Kingdom and Taiwan. The method has been extended to the removal of heavy metals from tailings dams, which has also reached full-scale with a plant near Canberra, to other industrial effluents, and more recently to sewage treatment. Successful pilot plant studies of the latter in Melbourne and Sydney have led to the decision to carry out a large-scale trial at Malabar, near Sydney.