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How does disinfection protect people from waterborne diseases?

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Diagram of a water treatment plant showing the process from water inlet through mixing, coagulation, flocculation, settling, filtering, chemical treatment with chlorine, storage, and high-lift pumping to the distribution system. — water purification Water from inlets located in the water supply, such as a lake, is sent to be mixed, coagulated, and flocculated and is then sent to the waterworks for purification by filtering and chemical treatment. After being treated, the water is pumped into water mains for storage or distribution.

Disinfection is the essential final step in the water purification process, specifically designed to protect public health by destroying pathogenic bacteria, viruses, and protozoa that cause waterborne diseases.12

By applying disinfectant agents—such as chlorine, chloramines, ozone, or ultraviolet radiation—water treatment facilities neutralize these harmful microorganisms before the water reaches consumers. In the case of chlorine-based methods, a residual concentration is often maintained throughout the distribution system to ensure the water remains safe until it reaches the point of use.123

This process is critical because unsafe water, often contaminated by microbial pathogens, is a leading cause of diarrheal diseases worldwide, which significantly impact global health and mortality rates. By effectively eliminating these biological threats, disinfection serves as a primary defense in preventing the spread of illness and ensuring a reliable, safe water supply.425