Before taking a bacteriological water sample, how long should water flow moderately from a faucet?

• A. 1 min
• B. 3 mins
• C. 5 mins
• D. 10 mins

Answer: (B)

When collecting a bacteriological water sample, you flush the faucet to replace any water that has been sitting in the pipes with fresh water from the distribution system. This helps remove stagnant water, sediments, and any near-faucet biofilm, so the sample reflects the actual quality of the supply rather than what’s been sitting in the plumbing. It also helps minimize the influence of residual disinfectants that could skew results.

Flushing for a moderate, practical duration—about three minutes—is long enough to purge the immediate stagnation and obtain a representative sample, but not so long as to waste water. Too short a flush may still contain stagnant water; a much longer flush generally doesn’t improve representativeness and wastes resources.