What is a grab sample in water testing?

A grab sample in water testing refers to a single sample of water collected at a specific time and place. This method is often used for situations where immediate results are needed or when assessing water quality at a specific moment, such as during a water quality incident or when testing for specific contaminants. Grab samples provide a snapshot of the water's characteristics at the time of collection, allowing operators to quickly evaluate water conditions.

In contrast, a composite sample involves collecting multiple samples over a designated period and combining them for analysis, which can provide a more comprehensive overview of water quality over time. Other sampling methods, like those analyzed by multiple labs or representing large volumes of water, do not fit the definition of a grab sample, as they involve different strategies for collecting and assessing water samples and data.