City drinking water is disinfected in two stages. Primary disinfection treats source water to kill bacteria, viruses, and other pathogens—almost always using free chlorine in Canada because it acts quickly and aggressively destroys harmful organisms. Because water must travel long distances through distribution pipes, cities add a residual disinfectant to keep it safe until it reaches homes. This is where chlorine vs. chloramine comes in.

Chlorine provides a strong, fast-acting disinfectant residual, but it dissipates quickly and reacts with organic matter in the system, reducing its effectiveness over long distances. Chloramine, created by combining chlorine and ammonia, behaves differently. It is a weaker but much longer-lasting disinfectant, remaining stable throughout the entire distribution network. Its persistence ensures consistent protection from the treatment plant to the tap, which is the main reason many cities adopt it.

Both disinfectants are effective, but each has drawbacks. Chlorine can cause noticeable taste and odour and may irritate sensitive skin or hair. Chloramine can cause issues for aquariums, medical equipment such as dialysis systems, and people with certain chemical sensitivities. It also interacts with some plumbing materials differently than chlorine, which has raised concerns in a number of communities. Both chlorine and chloramine are removed with activated carbon filtration, but chloramine removal requires catalytic carbon because of its greater stability.