What is the minimum chlorine residual required for effective primary disinfection?

The minimum chlorine residual required for effective primary disinfection is 0.1 mg/L. This level is important because it ensures that sufficient chlorine remains in the water to inactivate pathogens such as bacteria, viruses, and other microorganisms. Effective disinfection requires not just the presence of chlorine, but a measurable residual that can act over the contact time needed to achieve disinfection goals.

Maintaining a chlorine residual of 0.1 mg/L helps prevent regrowth of microorganisms in the distribution system and mitigates potential public health risks. It reflects a balance between providing adequate disinfectant levels while minimizing chlorine taste and odor. Therefore, this concentration is a standard recommendation in water treatment practices to ensure the safety and quality of drinking water.