EN ISO 17994:2014 PDF

Overview

EN ISO 17994:2014 - Water quality: Requirements for the comparison of the relative recovery of microorganisms by two quantitative methods - specifies an evaluation procedure and the mathematical basis for comparing two quantitative microbiological methods. Published by ISO and adopted by CEN (EN ISO 17994:2014), the standard is intended for methods with established performance characteristics (see ISO/TR 13843) and covers methods based on colony counts or most probable number (MPN) estimates. It focuses on assessing the average relative performance (relative recovery) between two methods; it does not provide precision data or single-laboratory verification procedures.

Key topics

• Scope and principle: Comparison of paired results from two quantitative microbiological methods for the same target organisms or groups.
• Confirmed counts and presumptive counts: Use of confirmed counts (presumptive count × confirmation coefficient) and handling of MPN or colony counts.
• Study design essentials: Requirements for sample types, number of samples, and participating laboratories in comparison trials.
• Data processing and calculations: Preliminary data editing, calculation of basic relative differences (natural-log scale), and computation of confidence intervals (half-widths).
• Evaluation criteria: Two-sided and one-sided evaluations against predetermined stipulated limits (confidence interval bounds, commonly referenced examples: 2L = 10% for drinking water, 2L = 20% for environmental waters).
• Reporting: Minimum contents of a test report and informative annexes (flowchart, example evaluations, sample-size derivation).

Applications

• Validation and comparison of a new or trial method against a reference or standard method for microbiological analysis of water.
• Design and analysis of interlaboratory comparison trials where paired measurements are collected.
• Regulatory or contractual assessments where stakeholders need evidence that two methods are not quantitatively different within predefined limits.
• Method transfer exercises and demonstration of equivalent recovery for microbial targets (e.g., indicator bacteria, pathogens) in drinking, recreational, or environmental water testing.

Who should use it

• Accredited water testing laboratories and quality managers
• Method developers and validation teams in microbiology
• Regulatory agencies and public health authorities
• Water utilities and environmental monitoring programs
• Standards bodies and interlaboratory study coordinators

Related standards

• ISO/TR 13843 - Guidance on validation of microbiological methods (performance characterization)
• ISO 8199 - General guidance on enumeration of microorganisms by culture

Keywords: EN ISO 17994:2014, water quality, relative recovery, microorganisms, quantitative methods, comparison study, MPN, colony counts, ISO/TR 13843.