Free chlorine residual values are based on a contact time of how many minutes?

Free chlorine residual values are typically based on a contact time of 30 minutes. This duration is significant because it allows sufficient time for chlorine to effectively disinfect water by inactivating pathogens. The established guideline indicates that a minimum of 30 minutes of contact time is necessary to achieve adequate disinfection levels, ensuring the chlorine has enough opportunity to interact with and neutralize microorganisms present in the water.

While shorter contact times may be considered in specific situations or under certain circumstances, for general water treatment practices, the standard 30-minute rule is crucial for ensuring that free chlorine levels can provide reliable and effective disinfection.