How long should a sample collector flush a line while collecting a Bacti sample?

When collecting a bacteriological sample for testing, it is essential to ensure that the sample is representative of the water supply and not contaminated by any stagnant water that may sit in the service lines. Flushing the line until water is being pulled from the main confirms that the sample is representative of the water quality in the distribution system, as it ensures that the water being sampled is fresh and has not been sitting in the lines.

This method minimizes the risk of contaminants and provides the most accurate representation of the water quality, which is critical for bacteriological testing. It verifies that the sample is collected from an active source, reducing the likelihood of introducing harmful bacteria from stagnant water.

In contrast, flushing for a specific time, such as one minute or five minutes, does not guarantee that the water has moved through the entire system sufficiently. Additionally, flushing until the water is clear might not be reliable, as it does not consider whether the water has reached a source that reflects the actual supply. Thus, flushing until water is being pulled from the main is the most effective approach for obtaining a quality sample for bacterial testing.