4.2.1 Assessment of the drinking water supply

Analysis of the water supply system, identification of potential hazards and risk assessment (described in detail in Section 3.2) are essential for good management of all supplies.

In the case of small supplies, initial steps would be to develop a simple flow diagram of the main features of the system (water sources, treatment or disinfection, service tanks and major piping) and to determine basic water quality characteristics. If groundwater is the source of supply, then chemical and microbial quality should be assessed as a priority. In some parts of Australia, concentrations of naturally occurring elements such as arsenic, fluoride and uranium, or nitrates from agricultural land uses, may exceed safe levels.

The water system should be inspected to identify likely sources of hazards. The greatest sources of microbial hazards are human and livestock wastes, and water systems should be inspected to determine the likelihood that this type of contamination will affect water quality. The discharge of septic waste and access of livestock to watercourses, or the proximity of either to supply bores, are likely sources of contamination.

Potential sources of hazards for water supplies can include:

• septic waste from on-site or communal wastewater systems

• human wastes from tourists, campers and others having access to water catchments

• animal faeces or dumped animal carcases

• effluent from factories, milking sheds and urban stormwater drains (which may contain partially treated sullage and toilet wastes)

• leakage or seepage from rubbish tips and landfill sites

• agricultural pesticides and fertilisers

• naturally occurring elements

• mining industry wastes.

Risk assessment, described in detail in Section 3.2.3, involves estimating the likelihood that a hazard will occur and the consequences if it does. The aim is to distinguish between high and low risks so that attention and resources can be directed towards those hazards that are most threatening. The risks associated with all hazards identified for a small water supply system should be assessed.