When collecting a distribution system sample, how long should the water be allowed to run prior to sample collection?

Allowing the water to run for a sufficient amount of time before collecting a sample is crucial to ensure that the sample reflects the quality of the water in the distribution system rather than water that may be stagnant in the service line. Running the water allows for the flushing out of any residual contaminants or sediments that may have accumulated in the pipes.

This flushing process helps to obtain a representative sample of the water that is actually being delivered to customers. The duration for running the water "as long as necessary to permit cleaning of the service line" emphasizes the importance of not rushing the sampling process but rather ensuring that what is collected accurately represents the water quality. This practice aligns with standard sampling protocols that prioritize obtaining high-quality samples for analysis, thus providing more reliable data for monitoring water quality in the distribution system.