FAC and TBR are metrics used to evaluate which environmental parameter in water systems after disinfection?

• A. Water flow rate and temperature
• B. Total bacteria count
• C. The amount of halogen present in potable water after disinfection
• D. Chlorine residual and related halogen content

Answer: (C)

The main idea is tracking the amount of halogen disinfectant left in the water after treatment. FAC (free available chlorine) shows how much chlorine remains available to continue disinfection, while TBR (total bromine residual) indicates how much bromine-based halogen is still present. Together, these metrics reflect the residual halogen content in potable water, which is what you monitor to ensure ongoing protection against microbes without overdoing chlorination. This isn’t about how fast water moves or its temperature, and it isn’t a direct measure of how many bacteria are currently present—the point is how much disinfectant remains in the water after treatment to maintain safety.