Why is chlorine used to disinfect water supplies?

Chlorine is used to disinfect water supplies because it effectively destroys pathogenic bacteria, which is essential for preventing the spread of waterborne diseases.1

The process, known as chlorination, involves adding chlorine or chlorine compounds to drinking water. A primary advantage of using chlorine is that a residual concentration can be maintained throughout the water distribution system, ensuring that the water remains safe until it reaches the point of use. While other methods like ozone disinfection exist, they do not leave a residual, making it more difficult to monitor the continued effectiveness of the treatment as water travels through pipes.23

Although chlorine can produce potentially harmful by-products when reacting with organic matter, these risks are minimized when it is applied after standard treatment processes such as coagulation, sedimentation, and filtration. Additionally, the use of chloramines—a combination of chlorine and ammonia—is an increasingly common alternative that provides a longer-lasting disinfecting effect and reduces taste and odor issues.2