The Standing Committee of Analysts

The Standing Committee of Analysts

Uncertainty of Measurement

The European Union (EU) Commission Directive 2015/1787, amending Annexes II and III to the EU Drinking Water Directive (98/83/EC), was officially adopted by the European Commission on 6 October 2015 and will come into force in the UK by amendments to the Water Supply (Water Quality) Regulations. The amending regulations introduce a requirement for uncertainty of measurement and limit of quantification as performance characteristics for analysis for the purposes of regulatory monitoring. The regulations remove the regulatory requirement for trueness, precision and limit of detection. The regulations state that trueness, precision and limit of detection may be used as an alternative set of performance characteristics to limit of quantification and uncertainty of measurement until 31 December 2019 to provide laboratories time to adapt to this change. It is the Drinking Water Inspectorate’s (DWI) role to regulate water companies in England and Wales to ensure the requirements of the Water Supply (Water Quality) Regulations, including analysis, are met. There is already a requirement for laboratories undertaking analysis for the purpose of compliance assessment to incorporate uncertainty of measurement calculations as part of the requirements of EN ISO/IEC 17025 (2005).

This document and the associated spreedsheets will ensure a consistent approach to calculation of uncertainty of measurement and limit of quantification across all laboratories in England and Wales that undertake analysis for the purposes of drinking water compliance.

File Type
Estimation of Uncertainty of Measurement for Chemical and Physico-chemical Determinands in Drinking Water
UoM-BB determinands table_Jan2018
UoM-BB calculations_Jan2018




The Standing Committee of Analysts (SCA) exists to provide authoritative guidance on methods of sampling and analysis of waters and effluents, sewage sludges, sediments, soils (including contaminated land) and biota. Where appropriate, guidance on the sampling and analysis of air will also be produced. The primary duty of SCA will be to develop and publish recommended analytical methods. This will not include the provision of advice on, or interpretation of results. All methods published by the SCA should be capable of satisfying a regulatory demand, be fit for purpose and represent best practice within the United Kingdom (UK).
However, validation data published with methods represents performance under a particular set of circumstances and is provided for illustrative purposes only. It is incumbent on users of SCA methods to assess performance on their equipment, in their laboratories, with their personnel.