Under no circumstances should a composite sample be collected for which type of analysis?

For bacteriological analysis, composite samples should not be collected because the nature of microbial populations in water can change significantly over time and due to different locations within a body of water. Bacteriological testing is typically conducted on grab samples, which represent a single point in time and location, ensuring that the analysis reflects the actual microbial content present at that moment.

Composite sampling involves taking several smaller samples over time and averaging them, which could dilute or mask the presence of bacteria that may be sporadic. When it comes to microbiological assessments, the concentration of pathogens can vary greatly over short periods or distances, making it critical to capture these fluctuations accurately through single, discrete samples rather than combining them into a composite. This ensures that any contamination or growth that may be present is fully represented in the sample being analyzed.

In contrast, other analyses like total dissolved solids, alkalinity, and turbidity are less affected by the transient nature of microbiological presence and can be aggregated without compromising the integrity of the results.