Which of the following is not commonly used to disinfect water?

The choice of fluorine as not commonly being used to disinfect water is accurate due to the fact that fluorine is primarily employed as a fluoridating agent rather than a disinfectant. In water treatment, fluorine compounds like sodium fluoride are added to help reduce dental caries in populations, promoting public health.

In contrast, chlorine, bromine, and iodine are widely recognized for their disinfectant properties. Chlorine is the most popular disinfectant used globally due to its effectiveness against bacteria and viruses and its ability to provide residual disinfection after treatment. Bromine is also used, particularly in hot tubs and swimming pools, due to its effectiveness in warm water. Iodine serves as a disinfectant as well, especially in emergency situations and for portable water purification, although it is not as commonly utilized for large-scale water treatment as chlorine or bromine.

Thus, while fluorine has its important role in water treatment regarding dental health, it does not function as a disinfectant like the others mentioned, making it the correct choice in this context.