Which method is usually preferred for disinfection of large water systems due to better distribution?

Chlorine gas is often the preferred method for disinfecting large water systems primarily due to its effectiveness in ensuring uniform distribution throughout the entire system. When chlorine gas is introduced into a water supply, it dissolves quickly and interacts readily with various pathogens, providing rapid disinfection.

The ability of chlorine to form chlorine residuals in the water is crucial as it not only disinfects the water but also helps to maintain a residual level that can inhibit microbial regrowth as water travels through extensive distribution networks. This property ensures that all points in the system, even those that may have lower water flow, receive adequate disinfection.

While other disinfection methods like ultraviolet light and ozone are effective in killing pathogens, they may not provide residual disinfection over time. Ultraviolet light, for instance, is limited to the point of application and does not remain active in the water, meaning any regrowth in the distribution system could occur after treatment. Ozone is also effective as a disinfectant but, similar to UV, lacks the ability to provide lasting residual disinfection.

Liquid chlorine could also be used effectively, but chlorine gas remains preferred particularly for large systems due to its storage and handling benefits, as well as its proven performance in extensive water systems.