ISO/TS 20612:2007

Overview

ISO/TS 20612:2007 - Water quality: Interlaboratory comparisons for proficiency testing of analytical chemistry laboratories defines criteria for designing, running and evaluating proficiency testing (PT) schemes in the fields of water, wastewater and sludge analysis. It focuses on interlaboratory comparisons used to assess laboratory competence for chemical and physicochemical determinands where measurement values show a degree of continuity. The Technical Specification complements general PT and accreditation guidance by setting sector-specific requirements for providers, participants and statistical evaluation.

Key topics and technical requirements

• Scope and applicability: Intended for chemical/physicochemical analytes; may be less suitable for biological/microbiological determinands where continuity is lacking.
• Proficiency test provider requirements: Providers should have documented quality management (aligned with ISO/IEC 17025 or ISO/IEC 17020) and relevant analytical expertise, plus advisory groups for specialist input.
• Proficiency test plan: Mandatory pre-defined plan covering staff, sample matrix, determinands, concentration levels, number of samples, containers, preservation, distribution, homogenization, homogeneity & stability checks, schedule, assigned-value method and evaluation procedures.
• Sample selection and preparation: Prefer real or spiked real samples that reflect routine matrices and concentration ranges; spiking is allowed but must not change the analytical difficulty unduly.
• Participant requirements: Only suitably equipped and staffed laboratories should participate; each lab should appoint a contact responsible for the PT.
• Statistical design & evaluation: Uses interlaboratory statistical methods (z-scores, reproducibility and repeatability considerations, variance functions). The document includes worked examples and annexes (Q‑method, repeatability s, variance function) to support fair, robust assessment.
• Minimum participants: If the assigned value is derived from participants' data, the number of laboratories should be sufficiently large - recommended to be never less than 12.

Applications and users

• Proficiency test providers developing water-sector PT schemes.
• Analytical chemistry laboratories seeking objective measurement of performance and evidence for accreditation.
• Accreditation bodies and regulators evaluating lab competence for water, wastewater and sludge testing.
• Water utilities and environmental consultants that rely on comparable, validated lab data.

Practical benefits include improved confidence in lab results, standardized PT design and fair cross-laboratory assessment, and support for accreditation decisions and regulatory compliance.

Related standards

ISO/TS 20612:2007 references and complements: ISO 13528, ISO/IEC Guides 43-1/43-2, ILAC Guide 13, ISO/IEC 17025, ISO 5725-1/2. These documents provide wider statistical methods, PT scheme operation and laboratory competence frameworks.