10.3.3 Long-term evaluation of aesthetic performance

The long-term evaluation of aesthetic performance is a system-wide assessment that includes evaluation of monitoring data for the distribution system, including the point of supply to consumers over a period against aesthetic guideline values, supplemented by all available operational, investigation and validation monitoring data from catchment to consumer.

The objective of the long-term evaluation is to understand system performance and confirm the robustness of the system to reliably deliver drinking water with characteristics that meet the physical and non-health-based chemical guideline values and/or requirements agreed with customers and other stakeholders. In addition, it is necessary to confirm that aesthetic water quality is not having an adverse impact on health-based system performance.

Review of aesthetic quality monitoring within the distribution system

When assessing and reporting the long-term performance of characteristics against aesthetic guideline values, each characteristic should be reported per water quality monitoring zone, listing the number of samples collected per zone, the minimum, maximum and mean result, and the number of results outside the relevant aesthetic guideline value. Any corrective actions that have been taken should also be listed.

The mean of the previous 12 months’ monitoring results should be compared to the aesthetic guideline value. If the mean for any aesthetic characteristic falls outside the guideline value, it should be further investigated to understand the reason for this outcome, and identify any trends that may be developing and the actions required to prevent recurrences. In such cases, investigative studies and additional monitoring may be required to improve characterisation of the water quality.

Review of operational monitoring – catchment to consumer

To ensure and/or improve aesthetic water quality performance and assess possible health impacts, review of operational monitoring data from catchment to consumer is required.

An important consideration in long-term evaluation is to assess if the overall performance of any aesthetic characteristic is likely to be associated with an adverse effect on the safety of the water supplied to customers (e.g. pH can affect chlorination effectiveness and the corrosiveness of the water). Typically this requires evaluating the aesthetic monitoring data in conjunction with other data, such as microbial monitoring data. If the safety of drinking water is unacceptably affected, then corrective actions should be included in the water quality improvement plan. If there is uncertainty about whether these characteristics are affecting system performance, additional operational monitoring should be planned.

The review should also assess the acceptability of the aesthetic quality of water received by consumers, taking into account that most non-health-based characteristics relate to the palatability and amenity of the water and, as such, that there is a degree of subjectivity involved in setting the guideline values for these characteristics. Where there is ongoing non-conformance with aesthetic guideline values, water suppliers should review customer complaints and consider consulting with customers to determine the impact.

Consumers notice and do not appreciate large variations in aesthetic water quality. Drinking water supplies subject to large variations in aesthetic quality should be assessed to identify the actions or investments needed to achieve greater consistency (e.g. selection of bore combinations, improved treatment). The decision to proceed with any aesthetic water quality improvements will depend on a number of factors including cost, technical difficulty, operator capability, and consumer feedback and willingness to pay for improvements. Where aesthetic quality improvements are programmed, progress on the improvements and their effectiveness should be reported.