Overview
ISO 13843:2017 - "Water quality - Requirements for establishing performance characteristics of quantitative microbiological methods" - defines how to characterize and document the performance of quantitative microbiological methods used for water testing. The standard focuses on establishing measurable performance characteristics (e.g., sensitivity, specificity, limits of detection, precision) that support subsequent method validation or verification. It applies to all types of water and emphasizes selective quantitative methods such as colony count, most probable number (MPN) and direct microscopic count, while noting special considerations for newer molecular methods (qPCR, FISH).
Key topics and requirements
ISO 13843:2017 provides procedures, experimental designs and guidance for determining method performance. Key technical topics include:
- Characterization vs verification: distinction between generating performance data (characterization) and demonstrating conformance in a specific lab (verification).
- Categorical performance: assessment of sensitivity, specificity, efficiency, selectivity, false positive/negative rates and relative recovery.
- Working range and limits: procedures to determine upper limits, and considerations for lower limits of detection for quantitative methods.
- Precision: experimental designs for repeatability (within-run), intralaboratory reproducibility and interlaboratory reproducibility.
- Robustness: assessment of effects due to changes in time, temperature and critical parameters.
- Uncertainty of counting: models and experiments for uncertainty in colony counts, MPN and microscopic counts.
- Study design guidance: sample selection, number of samples, confirmation procedures and worked examples.
- Annexes: normative and informative annexes cover mathematical models, assessment of limits, operational variability, uncertainty of counting and collaborative study designs.
Practical applications and users
ISO 13843 is used to produce robust, traceable evidence of how a quantitative microbiological method performs in real-world water testing. Typical uses:
- Laboratories performing method development, validation or single-laboratory verification.
- Manufacturers of microbiological test kits and instrumentation preparing performance dossiers.
- Accreditation bodies and regulatory agencies reviewing method performance claims.
- Environmental, drinking water and public health laboratories establishing routine quality assurance.
- Researchers comparing classical culture-based methods with molecular approaches (qPCR, FISH).
By following ISO 13843, organizations can better quantify method limitations (LOD, linear range), improve reproducibility, reduce false results and support regulatory acceptance.
Related standards
- ISO 17994:2014 - Water quality - Requirements for the comparison of the relative recovery of microorganisms by two quantitative methods (referenced in ISO 13843).
- ISO/TR 13843:2000 - earlier technical report replaced by ISO 13843:2017.
Keywords: ISO 13843, water quality, microbiological methods, performance characteristics, sensitivity specificity, repeatability reproducibility, limit of detection, validation, quantitative microbiology.