Validation, verification and comparison: Adopting new methods in water microbiology#

Until recently there has been little formal guidance on procedures for adopting new methods in water microbiology. However, the European Union Drinking Water Directive of 1998 specified methods that were to be used for the microbiological parameters, most being ISO methods, but allowed the use of alternative methods that were “at least as reliable”. At that time, there were no published procedures for demonstrating equivalency of performance between methods. Work commissioned by the UK Drinking Water Inspectorate (DWI) developed suitable analytical and statistical protocols for comparing microbiological methods. The statistical aspects have been refined and recently published as ISO 17994. ISO has also recently published guidance on the validation of methods for water microbiology (ISO/TR 13843), which gives guidance for developers of new media on what performance information is required. These developments provide a framework for the enhancement of validation and verification procedures within a laboratory’s quality system for evaluating new methods prior to their adoption. This paper overviews these developments in light of the author’s experience in their use and discusses issues relating to the analytical procedures and the statistical rationale employed (including the concept of “equivalency” of performance between methods).