For which type of analysis should a composite sample never be collected?

A composite sample should never be collected for bacteriological analysis because this type of analysis is highly sensitive to the presence of microorganisms, which can vary significantly over time and location in a water source. Bacteriological testing requires a representative sample that accurately reflects the current biological condition of the water at that specific moment.

Composite samples, which combine multiple samples collected over time or from various locations, can dilute the presence of bacteria and may mask contamination events. Since bacterial counts fluctuate, a single grab sample is preferred for bacteriological analysis to ensure that any present pathogens are accurately detected. Therefore, collecting a composite sample would compromise the reliability of the results for assessing microbial safety in water.