The disinfection of drinking water and municipal wastewater protects public health by destroying bacteria and viruses, thus helping to protect ecosystems and prevent the spread of waterborne disease. Chlorine is the most commonly used disinfectant for both drinking water and wastewater treatment, because of its effectiveness against a wide spectrum of disease causing organisms, relatively low cost, and high reliability. Chlorine can be applied to water directly as a gas, or through the use of chlorinating chemicals. A number of alternative disinfectants, such as chlorine dioxide, chloramines, ozone, and ultraviolet radiation, are also used to varying degrees.

Since September 11, 2001, water systems are giving greater attention to the security of their facilities. Many systems are conducting comprehensive "vulnerability assessments" and taking actions to protect against potential contamination of water supplies or disruption of service. Security considerations may influence how facilities transport, store and handle treatment chemicals, as well as the disinfection technologies they use. However, each disinfection technology has unique benefits, limitations, and costs, and individual water system operators must weigh these trade-offs and choose disinfection methods based on local water quality conditions and the needs and resources of the communities they serve.

The Canadian Water and Wastewater Association (CWWA) plays a critical role in the security of water and wastewater disinfection in Canada. CWWA recommends that all municipal water and wastewater services be prepared to face emergency situations in the operation of their infrastructure and services. The organization has a Water Protection Information Committee which supports CWWA in its work with international and domestic security agencies such as Public Safety Canada to ensure all municipal systems have access to the latest security information.

C4 and the Chlorine Institute support the goals of CWWA in this area and assist where possible with technical information and security information regarding chlorine developed in other jurisdictions. This information relates to both site security and transportation security issues.