It is recommended that the free chlorine residual at a customer's tap should be at least ________.

• A. A trace
• B. 0.1 mg/L
• C. 0.2 mg/L
• D. 0.5 mg/L

Answer: (C)

Maintaining a free chlorine residual at the customer’s tap is essential to keep water protected from microbial growth as it travels through the distribution system. A detectable residual shows there is still disinfection continuing to act after treatment. The commonly recommended minimum is 0.2 mg/L because it provides ongoing protection without causing unnecessary taste or odor issues. A trace or 0.1 mg/L would be too low to reliably guard against contamination, while 0.5 mg/L, though more disinfection-strong, can be unnecessarily high for most systems and may lead to taste concerns and higher disinfection byproduct formation. So, 0.2 mg/L is the appropriate minimum.