What is the FAC range for pools?

• A. 0.5-1.5 mg/L
• B. 1.0-4.0 mg/L
• C. 2.0-6.0 mg/L
• D. 4.0-8.0 mg/L

Answer: (B)

Free available chlorine (FAC) is the portion of chlorine in pool water that remains free to disinfect and oxidize contaminants. The tested range for FAC should be high enough to maintain a disinfectant residual under typical pool conditions (bather load, organics, sunlight) but not so high that it irritates eyes or skin or damages equipment. The range of 1.0 to 4.0 mg/L captures this balance: starting at around 1 mg/L ensures there is a reliable disinfection level even as chlorine reacts with contaminants, while staying under about 4 mg/L helps keep swimmer comfort and safety in check. Lowering FAC below 1 mg/L risks insufficient disinfection, especially in busy pools, and allowing FAC to approach or exceed 6 mg/L or 8 mg/L would be unnecessarily aggressive and more likely to cause irritation. So, the best-supported range for maintaining effective and safe disinfection in pools is 1.0–4.0 mg/L.