What is free available chlorine (FAC)?

Free available chlorine (FAC) refers to the portion of chlorine in the water that is not chemically bound to other substances and is readily available to disinfect and kill pathogens. This includes both hypochlorous acid and hypochlorite ions, which are the active forms of chlorine in water.

When chlorine is added to water, it can exist in different forms. Some chlorine may react with contaminants or other substances present in the water, becoming combined chlorine, which is less effective as a disinfectant. FAC is essential for maintaining water quality because its primary role is to eliminate harmful microorganisms, thus keeping swimming environments safe for users.

The other choices do not accurately represent what FAC is. Combined chlorine represents chlorine that has reacted with ammonia or organic compounds and is less effective for disinfection. Total chlorine includes both free and combined forms, which does not focus solely on the active disinfecting capability. The loss of chlorine due to sunlight exposure relates to the degradation of chlorine rather than defining what is available for disinfection. Understanding FAC is crucial for swim pool operators to ensure proper sanitation practices and effective pool maintenance.