What type of sample is necessary to determine the presence of coliform bacteria?

• A. Composite sample
• B. Grab sample
• C. Bulk sample
• D. Continuous sample

Answer: (B)

To determine the presence of coliform bacteria, a grab sample is necessary because it allows for the immediate collection of a water sample that can be tested for bacterial presence. Grab samples are typically taken at a specific point in time and are ideal for capturing a snapshot of the water quality at that moment. This is critical for detecting coliform organisms, which can indicate contamination and potential health risks; timely analysis of the sample is essential because coliforms, being sensitive indicators, may not persist if the sample sits for too long before testing.

While other sampling methods, like composite sampling, involve collecting multiple samples over a period, they may dilute or mask the presence of bacteria by averaging the results. This could lead to the failure to detect intermittent contamination events. Similarly, bulk samples are not suitable for immediate testing and may not accurately reflect the water quality. Continuous sampling, while valuable for certain types of analyses, is not the most efficient or effective method for detecting coliform bacteria due to the need for prompt results from a specific sample. Thus, the grab sample stands out as the most appropriate choice for this specific test.