1.1: Introduction to water treatment

Most Australian source waters require treatment prior to being supplied to consumers as drinking water. The level of treatment that is required will be a function of the quality of the source water and should be informed by a risk assessment process that is consistent with the approach described under Element 2 (Assessment of the drinking water supply system) of the Framework for Management of Drinking Water Quality (the Framework), which is detailed in Chapter 3 of the Guidelines.

Water treatment processes are covered by Element 3 (Preventive measures for drinking water quality management) and Element 4 (Operational procedures and process control) of the Framework.

Water treatment processes can be roughly divided into two groups of processes: the physical removal of particulate matter and other contaminants (that is, coagulation, sedimentation, clarification and filtration), and the inactivation of pathogenic microorganisms (that is, disinfection).

Some of the important concepts that need to be considered in relation to water treatment are:

• the application of multiple barriers (section 3.3.1), which helps ensure that a failure of one barrier may be compensated by the effective operation of the remaining barriers, particularly where multiple hazards need to be managed, thus minimising the likelihood of contaminants passing through the entire treatment system and being present in sufficient amounts to cause harm to consumers;

• identifying which treatment processes will be considered critical control points (section 3.3.2), and establishing target criteria and critical limits for each treatment process which is identified as a critical control point (section 3.4.2);

• preparing and implementing operational procedures (section 3.4.1) and operational monitoring (section 3.4.2) for each treatment process;

• preparing corrective action procedures (section 3.4.3) in the event that there are excursions in the operational parameters; and

• undertaking employee training (section 3.7.2) to ensure that the treatment processes operate to the established target criteria and critical limits.

The following Information Sheets provide an overview of the primary inactivation processes used to disinfect water to a drinking water standard. The information provided in the Information Sheets is general in nature and the specific disinfection processes for individual water supply systems should be determined by a risk assessment, and in consultation with water treatment specialists.