Disinfection of water is done to remove disease-causing microorganisms (pathogenic bacteria) rather than color, taste, or odor issues.

Introduction / Context:
Disinfection is a targeted step in drinking water treatment that aims to inactivate or kill pathogenic microorganisms. Aesthetics such as color, taste, and odour are addressed by other treatment stages (coagulation, filtration, activated carbon).

Given Data / Assumptions:

• Treated water must be microbiologically safe.
• Disinfection focuses on bacteria, viruses, and protozoa.
• Common agents: chlorine, chloramines, ozone, UV.

Concept / Approach:
Disinfection achieves pathogen log-reduction. It does not primarily remove color/taste/odour, which are addressed earlier or by adsorptive processes.

Step-by-Step Solution:

Verification / Alternative check:
Microbiological tests (e.g., total coliform absence) verify disinfection; aesthetic fixes alone cannot ensure safety.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming chlorine will fix taste/odour/minerals; underestimating required CT and residual maintenance; ignoring by-product control (THMs, HAAs).

Final Answer:
Bacteria (pathogens)