Before collecting a drinking water sample, how long should the sampling tap be flushed?

Flushing the sampling tap for 2 to 3 minutes before collecting a drinking water sample is crucial for ensuring that the sample reflects the quality of water that consumers actually receive. Flushing helps to remove stagnant water that may have been sitting in the plumbing, particularly in the tap or any connected pipes. This stagnant water may not represent the current water quality and could include contaminants or variations that do not accurately reflect the source water.

Additionally, flushing allows for the replacement of this stagnant water with fresh water from the system. A duration of 2 to 3 minutes is generally considered sufficient to ensure that any residual contaminants are flushed out and to achieve a more consistent and representative sample of the water that is routinely supplied to consumers.

This practice is supported by guidelines from various health and environmental organizations that emphasize the importance of collection techniques in preserving the integrity of drinking water quality assessments.