Social & Preventive Medicine Minimum recommended dose of “free” residual chlorine in water for routine chlorination (in mg/L)- A 0.5 mg/L for a contact period of 1 hr. B 0.5 mg/L for a contact period of 1/2 hr. C 1.0 mg/L for a contact period of 1 hr. D 1.0 mg/L for contact period of 1/2 hr. 💡 Explanation Minimum recommended dose of "free" residual chlorine in water for routine chlorination (in mg/L)- ✓ Correct Answer: A. 0.5 mg/L for a contact period of 1 hr.