In water distribution terminology, which term identifies biological agents that can cause disease and are a concern in water systems?

• A. Turbidity
• B. Dissolved Gases
• C. Hardness
• D. Pathogens

Answer: (D)

Biological safety in water systems centers on the organisms that can cause illness. The term that identifies these disease-causing biological agents is pathogens, including bacteria, viruses, protozoa, and parasites that may contaminate water and are the key targets of disinfection and treatment. Turbidity describes cloudiness from suspended particles, not the agents themselves; dissolved gases are about gases in solution and affect odor, taste, and corrosion; hardness relates to mineral content and scaling. So pathogens best captures the concept of biological disease-causing agents in water systems.