Public-health indicator organisms: The detection of coliform bacteria in a drinking-water sample is most directly an indication of the potential presence of which contamination source?

Introduction:
Coliform bacteria (especially fecal coliforms and E. coli) are used as indicator organisms in water quality monitoring. Their presence signals potential fecal contamination and the possible presence of enteric pathogens such as viruses, protozoa, and pathogenic bacteria that originate from human or warm-blooded animal waste.

Given Data / Assumptions:

• Indicator organisms are not necessarily harmful themselves but correlate with sanitary quality.
• Standard tests target total coliforms, fecal coliforms, or E. coli specifically.
• The context is potable water safety and public health protection.

Concept / Approach:
Detecting coliforms implies a route of fecal entry into the water supply (e.g., sewage intrusion, failing septic systems, cross-connections, or inadequate disinfection). While other contaminants may coexist, coliform detection specifically guides investigation of sanitary breaches and immediate corrective actions, such as boil-water advisories and system flushing with elevated disinfectant residuals.

Step-by-Step Solution:
Recognize coliforms as fecal indicator bacteria.Link positive results to contamination pathways from human/animal waste.Choose “human feces” as the most directly relevant contamination source among options.

Verification / Alternative check:
Public health frameworks require repeat sampling and, if confirmed positive for E. coli, immediate public notification because of the close linkage to fecal contamination and pathogen risk.

Why Other Options Are Wrong:

• Radioactive wastes, fertilizer, heavy metals: Not indicated by coliform counts.
• Decaying plants/animals: Can affect taste/odor but are not specifically indicated by coliform presence.

Common Pitfalls:
Assuming total coliform positives always mean fecal contamination; distribution system biofilms can sometimes harbor coliforms—hence confirmatory tests for fecal coliforms or E. coli are crucial.

Final Answer:
human feces