The Total Coliform Rule is based first on which criterion?

• A. Presence or absence of coliforms in a sample
• B. Density of coliforms in a sample
• C. Type of coliforms in a sample
• D. Presence and absence of coliforms in multiple samples

Answer: (A)

The test is anchored in a simple yes-or-no check: is total coliform bacteria present in the water sample? This presence serves as the initial signal that triggers further confirmatory testing and corrective actions to protect drinking water quality. The rule uses this binary indicator because it quickly flags potential contamination and prompts investigation of treatment and distribution integrity. It does not base the first decision on how many coliforms are present (density) or on the specific type of coliforms, and while patterns across multiple samples matter for compliance, the first criterion is the presence or absence in an individual sample.