A1.3 Assessment of water quality data

A review of historical data from source waters, treatment plants and finished water supplied to consumers can assist in understanding drinking water system characteristics and the identification of hazards.

Summary of actions

• Assemble historical data from source waters, treatment plants and finished water supplied to consumers (over time and following specific events).

• Assess data using tools such as control charts and trends analysis to identify trends and potential problems.

Water quality data should be reviewed both over time and following specific events (e.g. heavy rainfall, natural disasters) to identify those aspects of the system that require improvement. Water quality parameters that can provide useful information include:

• turbidity or particle counts

• microbial quality

• chemical quality

• algal counts

• naturally occurring organic matter

• colour

• pH

• disinfectant residuals

• disinfection byproducts.

Tools that may be useful in assessing data include control charts and modelling methods (e.g. using temporal overlays of water quality records and climatic information). In some cases, awareness of potential problems or hazards can be difficult because events occur gradually or result from cumulative effects. Trends analysis can be a valuable tool for recognising the accumulation of gradual changes and for predicting where things may be going wrong.