4.1 This guide establishes basic requirements for water and environmental laboratories that generate and report test chemical analyses that the laboratory client desires to be traceable to the SI or to certified reference materials traceable to the SI (Note 1). Traceability of chemical analyses is important because it provides a uniform basis for the comparison of results from different measurement systems and because it relates those results to our current knowledge of physical laws (Note 2).

Note 1: A certified reference material traceable to the SI is a certified reference material whose value can be related to realizations of the SI units through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty.

Note 2: Not all chemical analysis results can be traceable to the SI or to certified reference materials traceable to the SI, for example, turbidity or total suspended solids.

4.2 Many waters-related laboratories comply with ISO/IEC 17025 and participate in proficiency testing programs. Laboratories that are connected to the same accreditation bodies and proficiency testing providers can be expected to report statistically similar results on the same sample. However, some test methods and some certified reference materials are not supported with data traceable to the SI. Therefore, fully compliant laboratories that are not connected to the same providers may report statistically different chemical analysis results if they use the same nontraceable test method on the same sample. This problem can be minimized if they use test methods, measurement devices, and certified reference materials that are traceable to the SI, where available.

4.3 Although some standard test methods and certified reference materials provide evidence of traceability to the SI, many others do not. Therefore, not all laboratories can be expected to universally meet all requests for traceable analyses until the traceability of more test methods and certified reference materials is recognized through appropriate documentation.

4.4 The primary significance of this guide is that it establishes a consensus that, in order for a laboratory to generate traceable measurements, it must (1) have a clear understanding of the needs of the user of the traceable measurements, (2) comply with the internationally accepted quality-system requirements included in ISO/IEC 17025, (3) use test methods, measurement devices, and certified reference materials that have been shown to be traceable to the SI, and (4) be able to demonstrate that the measurement system was in statistical control at the time the measurements were made.

4.5 It is expected that this guide will be used by Committee D19 in setting policies for the technical content of its standards that are designated to be usable to generate traceable chemical analyses.

1.1 This guide sets a protocol for generating and reporting chemical analyses that are traceable to the International System of Units (SI) or to certified reference materials, in laboratories that serve the water and environmental industry.

1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.