Iodine has been used to disinfect water for a long time. It is used in concentrations between 2.5 ppm to 7 ppm. 


Besides iodine, there is a long list of chemical compounds used as drinking water disinfectants- chlorine being one of them. For the extensive list, you can refer this site : 

http://www.lenntech.com/processes/disinfection/what-is-water-disinfection.htm