The detection of vibro cholera in public drinking water is a sign of

Analyze the question: Vibrio cholerae is the bacterium that causes cholera. The question asks what its detection in public drinking water indicates.

Concept: Vibrio cholerae is spread through water or food contaminated with human faeces. It does not occur naturally in clean, treated water. Finding it there means the water has been contaminated, usually by sewage or other waste. That is the definition of water pollution (specifically, biological pollution).

Step-by-step evaluation:

• A. Clean water: Wrong. Clean water would not contain disease-causing bacteria.
• B. Outbreak of disease: This is tempting. However, detecting the bacterium only shows that contamination is present. It does not prove that people are already sick. It is a warning of risk, not proof of an outbreak.
• C. Water pollution: Correct. The presence of a pathogen from faecal matter shows the water source is polluted.
• D. Decayed organisms in the water: Wrong. Cholera bacteria come from infected human waste, not from decaying organisms.

Exam tip: Distinguish an indicator from a consequence. A pathogen found in water indicates pollution. The disease outbreak comes afterwards, when people drink that water. Words like "detection" or "presence" usually point to the cause or condition (pollution), not the result (outbreak).