What disinfectant is commonly used for large public water supplies?

Chlorine is a widely used disinfectant for large public water supplies due to its effectiveness in killing a broad spectrum of pathogens, including bacteria, viruses, and parasites. Its long-lasting residual effect also helps maintain water safety over time, as it continues to disinfect even after being added to the water supply. Chlorine is cost-effective and can be easily monitored and controlled, making it a popular choice for water treatment facilities.

Other options, while they have certain applications in water treatment, are not as commonly used for large-scale public water supplies. Ultraviolet rays can effectively disinfect water but do not provide a residual disinfectant effect, meaning they do not protect the water once it leaves the treatment facility. Ozone is also a powerful disinfectant but is more expensive and less stable than chlorine, requiring on-site generation and immediate use. Floe is not a disinfectant but is instead related to coagulation processes used to help settle particulate matter in water; it does not serve the purpose of sanitizing water supplies.