9.2.3 Catchment-to-consumer monitoring

Assuring the safety of drinking water requires an effective monitoring strategy that is preventive rather than reactive, and that aims to promote an understanding of the entire water supply system. An integrated approach to monitoring incorporates all aspects of the water supply system, including catchment and source water, treatment processes, the distribution system and consumers, to provide key information on system management and operation.

Source water

Effective system management requires knowledge of the source water (be it surface, ground or sea water) and the characteristics of the associated catchment area. Source water monitoring assists a water supplier in understanding what hazards are possible and the contamination challenge (i.e. the level of risk) they present.

Source water monitoring can also be preventive, in that it can be developed to provide an opportunity for real-time process control and the prediction of potential contamination; for example, concentration spikes of microbial pathogens associated with storm or heavy rain events. Early warning monitoring should be established to capture any changes from normal baseline levels, which in turn would trigger an appropriate response; for example, closing intakes or using alternative sources if available, changing treatment practices, increasing vigilance of system operation within specifications, and increased monitoring throughout the system (Wu 2004, Gullick et al. 2003).

Where a new drinking water source is to be brought on line (either adding to an existing water supply system, or as part of a new one), a range of monitoring and other background investigations are needed to inform hazard identification and risk assessment for the supply system. Monitoring requirements will be influenced by the characteristics of the water source and catchment. Types of monitoring to be considered include:

• microbiological monitoring based on potential sources of faecal contamination (e.g. sewage and septic waste, livestock);

• microbiological and chemical monitoring to assess intermittent or seasonal pollution patterns;

• chemical monitoring based on identified agricultural, mining, industrial and urban pollution sources;

• chemical monitoring based on geological features (particularly for groundwater sources);

• identification of existing land uses and planned developments.

Further information on the monitoring considerations for source waters can be found in the Appendix to this document; in Australian Guidelines for Water Quality Monitoring and Reporting (ANZECC and AMRCANZ 2000); in the Cooperative Research Centre for Water Quality and Treatment (CRCWQT) reports 11, A Guide to Hazard Identification and Risk Assessment for Drinking Water Supplies (2004), and 37, Strategic Water Quality Monitoring for Drinking Water Safety (2007); and in the CRCWQT and Water Quality Research Australia report 78, Risk Assessment for Drinking Water Sources (2009).

Water treatment plant

Monitoring of treatment processes and barriers is fundamental to a preventive strategy for drinking water safety. The advantage of monitoring treatment performance is that, if set up correctly, ineffective treatment processes (e.g. inadequate disinfection, shortening of filter runs, degraded filtered water quality) can be identified and acted upon in close to real-time, to prevent potentially contaminated water from reaching consumers. To help ensure that unsafe water is not delivered to consumers, monitoring results need to be promptly evaluated and reported and, where appropriate, corrective actions need to be implemented immediately.

Box 9.3 provides an example of a situation where failure to respond to changes in treatment plant performance contributed to an outbreak of waterborne disease.

If the source water challenge and water treatment capabilities are understood, if attention is focused on understanding treatment performance, and if performance is monitored continuously, this provides a high level of assurance of drinking water safety.

Box 9.3

Importance of monitoring treatment performance

In North Battleford, Canada, in 2001, poor treatment performance was observed for a prolonged period after maintenance work on the solids contact unit (SCU). When the SCU was brought back on line, it was achieving minimal clarification due to difficulties in re-establishing an effective floc blanket. This, along with filtration that was not optimised, resulted in treated water turbidities being much higher than usual. Given the poor treatment performance and the known vulnerability of the river water source to contamination by Cryptosporidium parvum, operational staff should have recognised the seriousness of the risk and informed public health officials. Although regulatory requirements were not exceeded, if the normal range of raw water turbidity and the implications of poor turbidity removal been properly understood, appropriate actions could have been taken. As it was, this poor performance continued for several weeks and a breakthrough of C. parvum occurred, ultimately affecting between 5800 and 7100 people (Laing 2002).

Distribution system

Good design, management and integrity of distribution systems are essential for maintaining water quality. Monitoring programs should consider the potential for stagnation and ingress of contamination through faults in the distribution system. Stagnation and growth of biofilms can occur in poorly designed and operated distribution systems, while ingress of contamination can occur through tanks, reservoirs and pipes, cross-connections to the pipe network, and poor control of repairs or installation of new mains. Monitoring the integrity of the distribution system, and the quality of water supplied to consumers, is necessary to confirm that drinking water quality is maintained.

Consumers

Monitoring consumer satisfaction is another important surveillance mechanism. Consumers are located throughout distribution systems and their feedback can be directly related to the quality of drinking water supplied. They can provide timely information on potential problems, particularly within the distribution system, that may otherwise go unidentified.