When collecting a water distribution sample for bacteriological testing, how long should water be allowed to run before filling the sample bottle?

When collecting a water distribution sample for bacteriological testing, it is essential to allow the water to run long enough to clear any stagnant water that may be present in the service line. This is important because stagnant water can contain higher concentrations of contaminants that could lead to inaccurate testing results. By letting the water run until the service line is cleared, the sample collected will better reflect the quality of the water that is supplied to consumers.

Other choices, such as specific time durations like 15 seconds, 30 seconds, or 2 minutes, may not be sufficient or may overly prolong the sampling process without ensuring that stagnant water is completely removed. Therefore, allowing the water to run "as long as necessary to permit clearing of the service line" is the most appropriate approach to ensure accurate testing for bacteriological quality.