Different representations
A grab sample represents a particular collection point and time. A composite combines material according to a defined plan. They answer different questions and cannot be exchanged simply for convenience.
Check parameter requirements
Preservation, stability and program instructions affect which collection approach is appropriate. Include the permit or monitoring plan when the scope is being set.
Document the design
Record collection locations, timing, increments and the basis used for any composite. Keep the final sample identity tied to the source collection records.
Plan the bottle and handling path
The sampler and laboratory should work from the same container, preservation and delivery instructions. Changes in the collection plan need review before the sample is treated as equivalent.
Related testing & guidance
Technical & service references
Vanguard water-testing menuEPA: Clean Water Act method questionsEPA: Drinking-water analytical methodsSource review: November 8, 2026. The agreed method and project scope govern the testing.