Which term identifies biological agents that can cause disease and are a concern in water distribution?

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

Answer: (D)

Biological agents that can cause disease in humans are called pathogens. In a water distribution system, pathogens are the primary safety concern because even small amounts can make people sick if disinfection and treatment fail or are insufficient. Pathogens include organisms like bacteria, viruses, and protozoa (for example Giardia or Cryptosporidium) that water utilities work to inactivate or remove through treatment processes and residual disinfection. The other terms describe non-biological aspects of water quality: turbidity is the cloudiness from suspended solids and can signal potential contamination but isn’t itself a disease-causing agent; dissolved gases are gases dissolved in water; hardness is the mineral content like calcium and magnesium. So the term that identifies the disease-causing biological agents relevant to water distribution is pathogens.