Cooling water tower systems should be treated to limit the growth of what primary microbiological contaminant?

• A. Escherichia coli
• B. Staphylococcus aureus
• C. Legionella sp.
• D. Pseudomonas aeruginosa

Answer: (C)

The key idea here is that Legionella bacteria are the primary microbiological concern in cooling water towers because these systems aerosolize water, creating tiny droplets that can be inhaled. Legionella thrives in warm water, biofilms, and environments where disinfection is challenging, often hiding inside amoebae which protects it from standard sanitizers. Inhaling contaminated aerosols can cause Legionnaires’ disease, a serious pneumonia, or Pontiac fever, so preventing its growth and spread is the main objective for these systems.

Other organisms can be present, but they are not the central hazard driving cooling tower treatment. Escherichia coli signals fecal contamination rather than the aerosol-related health risk specific to towers. Staphylococcus aureus is typically a skin-associated organism and not the primary inhalation threat from tower aerosols. Pseudomonas aeruginosa can inhabit water systems and cause infections in vulnerable people, but the disease risk from Legionella in the context of cooling towers is the principal concern and the primary target of control measures.