ISO 5667-20:2008 establishes principles, basic requirements, and illustrative methods for dealing with the use of sample data for decision making based on the assessment of the confidence that water quality: meets targets and complies with thresholds; has changed; and/or lies in a particular grade in a classification system.

ISO 5667-20:2008 also specifies methods for preliminary examination of the sensitivity of decisions to error and uncertainty, although it does not cover the full range of statistical techniques.

ISO 5667-20:2008 provides general advice on decision making related to constraint formulation for expression of thresholds and targets and the form and scale of sampling programmes.