Which of the following is the minimum sample size for total coliform analysis?

• A. 100 ml
• B. 1 ml
• C. 10 ml
• D. 1 liter

Answer: (A)

In total coliform testing, the amount of water you analyze is tied to how the methods are designed and how results are reported. The standard procedures (like membrane filtration or most probable number methods) are validated for a 100 mL sample, and results are interpreted per 100 mL. This volume provides enough organisms to detect contamination without making the test impractical.

Using a smaller volume would reduce the chance of catching low-level contamination, leading to falsely low or undetectable results. A larger volume isn’t required for routine testing and would just add handling time and complexity without changing the fundamental detection capability for standard methods. Therefore, 100 mL is the minimum typically used.