Which statement about disinfecting water is true?

The statement that contact time varies by the method used is accurate because different disinfection methods have distinct requirements for the time the disinfectant must come into contact with the water to effectively eliminate pathogens. For example, chlorine disinfection typically requires a specific minimum contact time based on factors such as water temperature, pH, and the concentration of chlorine present. In contrast, UV light disinfection is influenced by the intensity of the light and the clarity of the water, which can also alter the effective contact time needed for disinfection.

Understanding these variations is crucial for water operators, as ensuring the proper contact time for the chosen disinfection method is essential for meeting health standards and protecting public safety. This knowledge helps prevent waterborne illnesses and ensures the treated water meets regulatory compliance.