Water quality sampling

A laboratory can accurately measure what arrived in a bottle without that bottle representing the water condition a decision concerns. Sampling therefore begins with the question: which source, period, location and constituent are being characterized? A process check, discharge compliance sample and environmental survey can need different designs. The ISO 5667 family addresses this field-to-laboratory relationship. Selecting a sampling approach and selecting an analytical method are connected decisions, but neither one can stand in for the other.

ISO Open Data identifies Part 1 as programme-design guidance and Part 3 as requirements for preservation, handling, transport and storage within its scope. A reference to the series without a part gives little information about the actual work. Site-specific conditions and the analytical objective remain essential. Part 1 does not provide detailed instructions for every sampling situation, while Part 3 is particularly relevant when samples must travel to a laboratory instead of being analysed on site.

Selected records: ISO 5667-3:2024 (edition 6, publication record 2024-03-29); ISO 5667-1:2023 (edition 4, publication record 2023-03-14). Part 1 is guidance on sampling programmes and techniques; Part 3 specifies general requirements for sample preservation and handling within its stated scope. Other parts address particular situations. The selected Part 3 scope excludes ecotoxicological and biological assays, passive sampling and microplastics from that document, directing those subjects to separate references. The records were checked on 19 October 2026 in ISO Open Data.

For an industrial discharge investigation, the organization first identifies the discharge points and the period the results must represent. The field team and laboratory then agree the analytes, containers, preservation arrangements, transport and receipt criteria before collection. A documented handover connects the sampling plan to the laboratory request. If the process changes during collection or a sample arrives outside agreed conditions, that event belongs in the result’s interpretation. A neat chain-of-custody form cannot compensate for an unsuitable sampling design.

For applicable U.S. Clean Water Act reporting, 40 CFR 136.3 identifies approved procedures and includes parameter-specific preservation and holding-time provisions. EPA’s methods directory separately lists approved, optional and alternative-method resources. ISO 5667 is not automatically an approved replacement for every procedure in that programme. The permit, analyte and applicable rule determine the required route. Drinking-water programmes and other national systems need their own legal and method checks rather than borrowing this example without qualification.

Can the sampling location and timing be reconciled with the purpose of the investigation? Are grab or composite arrangements, field observations and deviations identifiable? Does the laboratory know the requested analyses before containers are selected? Are collection time, preservation, transport and receipt conditions traceable? A report needs an intelligible relationship to these records, especially where a result is close to a decision limit. Method-specific requirements take precedence over an assumption that one container or storage condition suits all constituents.

The central finding is that representativeness and sample integrity are different sources of confidence. Excellent preservation cannot repair a sampling location that misses the relevant process condition; a representative collection can still be compromised before analysis. This reference does not prescribe universal preservation temperatures, acidification, storage times or collection intervals. Such details depend on the analyte, method and regulatory programme. The public sources support a structured evidence review, not an assurance that any sample labelled “ISO 5667” is suitable for every purpose.

Testing and calibration laboratories addresses the competence behind an analytical result. Measurement uncertainty helps explain measurement interpretation, while the materials and construction subject provides related technical references. Use test evidence assessment to examine whether a report can be connected to the sampling location, date, collection method and handling record relevant to the decision.

Official sources and bibliographic records were checked on 19 October 2026. Licensed ISO scope metadata supports the family description. The EPA and eCFR sources address a particular U.S. regulatory programme, not universal instructions for every water sample. ISO metadata is attributed to the iso_deliverables_metadata dataset under ODC-By 1.0. The explanation and examples are original NCQM analysis. Send a correction request identifying the reference, disputed statement and official supporting evidence.