ISO 11352:2025

Overview

ISO 11352:2025 - Water quality - Estimation of measurement uncertainty based on validation and quality control data - provides a practical, top‑down framework for estimating measurement uncertainty for quantitative chemical and physicochemical methods used in water analysis. Designed for single laboratories, it uses validation results and routine internal/external quality control data to quantify both random and systematic components of uncertainty. The approach is consistent with ISO/IEC Guide 98‑3 and is largely based on Nordtest TR 537 (with input from QUAM and Eurolab TR 1/2007).

Key topics and requirements

• Scope and applicability: Applies primarily to quantitative measurement procedures in water analysis; approach can be adopted in other chemical analysis areas. Qualitative procedures are excluded.
• Top‑down methodology: Emphasizes using existing validation and routine quality control data rather than a full bottom‑up component analysis.
• Data sources for uncertainty estimation:
  • Validation studies (for initial estimates)
  • Internal quality control (control charts, pooled standard deviations)
  • External quality assessment / interlaboratory comparisons
  • Reference materials and recovery experiments for bias assessment
• Precision and bias assessment:
  • Evaluation of within‑laboratory reproducibility (intermediate precision)
  • Procedures for estimating bias from certified reference materials and participation in proficiency tests
  • Updated requirement for reproducibility data (noted change from a minimum of 8 to 20 replicates for components except first estimations)
• Uncertainty calculation:
  • Combining within‑laboratory reproducibility and bias into a combined standard uncertainty
  • Deriving an expanded uncertainty using an appropriate coverage factor
  • Guidance on initial estimation and reporting of uncertainties
• Supporting material:
  • Annexes covering range division for constant absolute vs relative uncertainties, pooled standard deviation estimation, and worked examples

Practical applications and users

ISO 11352:2025 is essential for:

• Environmental and water-testing laboratories needing robust, defensible uncertainty statements for chemical and physicochemical analytes
• Quality assurance managers and laboratory directors preparing reports for regulatory compliance or accreditation (e.g., ISO/IEC 17025)
• Analysts and method developers who require routine, data‑driven uncertainty estimation without advanced metrology expertise
• Regulators and third‑party auditors evaluating method performance claims and measurement traceability

Benefits include clearer reporting of result reliability, improved method validation workflows, and alignment with international metrology guidance.

Related standards

• ISO/IEC Guide 98‑3 (GUM principles)
• Nordtest TR 537 (basis for the top‑down approach)
• QUAM and Eurolab TR 1/2007 (supporting guidance)
• ISO/IEC Guide 99 (VIM) and ISO Guide 30 (reference materials)

Keywords: ISO 11352:2025, measurement uncertainty, water quality, validation data, quality control data, within‑laboratory reproducibility, bias estimation, combined standard uncertainty, expanded uncertainty.