Bacterial particle attachment and subsequent protection from disinfection: techniques of investigation and application to Melbourne's potable water supply

Melbourne's water distribution network is one of few in the world where the majority of drinking water is not filtered. This is due to the high quality of source water, which is collected from protected forested catchment areas. The unfiltered water undergoes a chlorination disinfection process, followed by fluoridation (to prevent tooth decay) and neutralisation (using alkaline lime). Recently, several studies have demonstrated that attachment of potentially disease-causing micro-organisms to particles may provide protection from disinfection processes. The risk of inadequate disinfection as a result of this is considered to be low, but is of significance to any unfiltered water supply and therefore should be further investigated. The difficulties in clearly assessing the risks of a particular system are numerous given the complexities inherent to any natural environment. As investigation of particle attachment has evolved, so too have the techniques of investigation. This review article explores the issue of particle-conferred protection and its applicability to unfiltered, chlorinated drinking water systems, and examines Fluorescence in situ hybridisation (FISH) as a future method of investigation.