10.1 Introduction

Monitoring data are generated from various sources, such as continuous operational monitoring, field measurements, grab samples, and observational activities. Results from both operational monitoring and verification of drinking water quality should be evaluated over both the short and long term. Results should be documented systematically, and a system of regular reporting of results to relevant staff, departments and external stakeholders (e.g. regulators) should be implemented.

In the short term, monitoring results should be reviewed promptly to assess performance against target criteria and critical limits, guideline values, microbial health-based targets or agreed levels of service. Where results indicate that established criteria, such as critical limits, have been exceeded or deviated from, or control of the process has been lost, immediate corrective action is required.

The objective of the long-term review of monitoring data is to look at overall system performance in order to enhance understanding of recognised problems, identify any emerging problems and trends, and evaluate the risk to public health and the need for water quality improvement projects. Long-term evaluation of monitoring data can provide confirmation of the hazard identification and risk assessment process, and it assists in corroborating or modifying the assumptions made in the previous risk assessment, as well as increasing system knowledge. It also serves an important due-diligence function with respect to protecting public health, and it contributes to consumer and stakeholder confidence.

For the purposes of this chapter, “short-term evaluation” refers to the routine review of a single monitoring result, or a time-limited (for example, 24 hours) review of on-line monitoring data. “Long-term evaluation” refers to the review of data and the assessment of performance over a time period, typically 12 months (but this could be shorter for critical control points).