Which disinfectant is known for remaining as a residual longer in the system?

• A. Chloramines
• B. Free chlorine
• C. Ozone
• D. Chlorine dioxide

Answer: (A)

Disinfectant residual refers to the amount of disinfectant left in the water to keep protecting against microbes as it moves through pipes. Chloramines stay in the water longer because they are formed when chlorine reacts with ammonia, creating a more stable, slower-acting disinfectant. This stability means chloramines persist as a residual in the distribution system, helping maintain protection between treatment plants and consumers. In contrast, free chlorine acts strongly but dissipates more quickly due to reactions with organic matter and other substances. Ozone works fast but doesn’t leave a lasting residual, and chlorine dioxide, while useful, typically doesn’t persist as long as chloramines. Therefore, chloramines are the disinfectant known for remaining as a residual longer in the system.