How does ammonia in water affect chlorine residuals in the distribution system?

• A. Ammonia reacts with chlorine to form chloramines, which are weaker disinfectants but more persistent.
• B. Ammonia strengthens chlorine as disinfectant.
• C. Ammonia has no effect on chlorine residuals.
• D. Ammonia removes chlorine through sedimentation.

Answer: (D)

Ammonia in water reacts with chlorine to form chloramines, which changes how chlorine residuals behave in the distribution system. When chlorine is added, ammonia consumes some of the free chlorine to create chloramines (such as monochloramine, dichloramine, and traces of trichloramine). These chloramines are weaker disinfectants than free chlorine, but they are more persistent, so the system shifts from a free-chlorine residual to a combined-chlorine residual that lingers as water moves through the network. This explains why the presence of ammonia lowers the immediate strength of disinfection while maintaining a longer-lasting residual.

Ammonia does not strengthen chlorine, nor does it remove chlorine through sedimentation, and it clearly affects chlorine residuals by forming chloramines.