3.11.1 Long-term evaluation of results

Summary of actions

• Collect and evaluate long-term data to assess performance and identify problems.

• Document and report results.

The systematic review of monitoring results over an extended period (typically the preceding 12 months or longer) is needed to:

• assess overall performance against numerical guideline values, microbial health-based targets, regulatory requirements or agreed levels of service

• identify emerging problems and trends

• assist in determining priorities for improving drinking water quality.

There will inevitably be occasions of non-conformance with operational criteria or numerical guideline values. Each event will need to be assessed and responses determined.

Mechanisms for evaluation of results should be documented, with responsibilities, accountabilities and reporting requirements defined. Useful tools to enhance the interpretation of data sets include statistical evaluation of results and graphs or trend charts using a ‘control chart’ format (see Information Sheets 3.1 to 3.4).

Evaluation of results should be reported internally to senior executive, and externally to consumers, stakeholders and regulatory authorities in accordance with established requirements (see Section 3.10.2). Providing assurance that data are reviewed regularly and that improvements are made in response to identified problems will contribute to consumer confidence.

Section 10.3 provides further guidance on assessing long-term system performance.