Delivered water must have what free chlorine residual?

• A. 0.0 mg/L
• B. 0.3 mg/L
• C. 1.0 mg/L
• D. 2.0 mg/L

Answer: (B)

Keeping a free chlorine residual in delivered drinking water is essential to maintain disinfection as water travels through the distribution system. A measurable residual acts as a protective barrier against microbial growth and ensures the water remains disinfected up to the tap. The commonly required minimum is about 0.3 mg/L, which represents the level needed to provide ongoing protection without being excessive.

Zero residual would mean no ongoing disinfection, increasing the risk of contamination. Residuals of 1.0 or 2.0 mg/L are higher than the minimum and can affect taste, odor, and pipe materials; they’re not the standard minimum, though they may be used in specific situations. So, 0.3 mg/L is the appropriate minimum delivered-water residual.