A grab sample typically requires what action before collection?

A grab sample typically requires the flushing of the tap before collection to ensure that the sample accurately represents the water quality of the system being tested. Flushing provides a means to remove any stagnant water that may have been sitting in the pipes or fixtures. This stagnant water may contain contaminants or altered water chemistry that does not reflect the actual quality of the water supply, which could lead to misleading results. By flushing the tap, analysts can obtain a sample that is more representative of the water in the distribution system at the time of collection.

In contrast, simply collecting a sample without flushing might not yield reliable data, while cooling the sample or allowing the water to sit does not contribute to obtaining a representative sample. Flushing is a critical initial step to ensure that the sample represents the current conditions of the water being tested.