10.2 Assessing safety: short-term evaluation of monitoring

Monitoring results should be reviewed promptly and assessed against specified operational criteria, guideline values, microbial health-based targets and agreed levels of service, or previous results, to ensure that preventive measures are functioning effectively and the drinking water quality supplied to consumers is acceptable. Monitoring results that fail to meet established criteria indicate a potential break in process control, and corrective actions are required to resolve the issue and regain control.

Those responsible for interpreting monitoring results and activities should have a sound understanding of the assessment process and the necessary responses, and should be familiar with any communication protocols. A considered approach to responding to potential failures should be developed and documented in advance, and should include any instructions on system investigation, additional monitoring, required adjustments upstream or downstream, and process control changes. The objective of the response is to re-establish the system within operating specification as rapidly as possible.

Immediate response and notification of the relevant health authority or drinking water regulator is required if there is a significant system failure that could pose a health risk or seriously affect water quality (e.g. non-conformance with critical limits, positive detections of E. coli within the distribution system, health-based chemical detections above the relevant guideline value). Incident and emergency response plans should be developed to deal with these failures. These plans will be particularly important for times when normal corrective actions cannot re-establish operational performance quickly enough to prevent drinking water of unacceptable quality from reaching consumers (see Section 3.6.2).

A process should be established for documenting and evaluating an event or incident, in order to identify opportunities for improvement. As necessary, the incident should also trigger further investigation, including a long-term review of relevant characteristics, to identify the underlying nature of any problems.

The following sections provide guidance on evaluating and responding to monitoring results from critical control points and other operational monitoring, as well as microbial, chemical and physical monitoring of the quality of drinking water as supplied to consumers.