New Mexico Water Operator Level 4 Practice Exam

Free chlorine is the active disinfectant form that acts quickly to inactivate microbes, giving rapid disinfection. However, its residual doesn’t last long in the distribution system because it reacts with organic matter, ammonia, and other compounds. Chloramines form when chlorine reacts with ammonia; they are more stable and persist longer in the water, providing a longer-lasting residual. They are generally less potent as disinfectants, so they require longer contact times to achieve the same level of inactivation, but they tend to form fewer disinfection byproducts and can have different taste/odor implications. This combination—fast, strong disinfection but short-lived residual versus slower disinfection with a longer-lasting residual and fewer byproducts—best differentiates free chlorine from chloramines.