Chlorine inactivates most pathogens that cause diarrheal disease in humans. This table (PDF - 129KB) details the effectiveness of chlorine against disease-causing bacteria, viruses, and protozoa. The Ct factor can be used to compare the effectiveness of chlorine against different pathogens, and is calculated by multiplying the concentration of chlorine needed to inactivate a certain percentage of the pathogens by the time the pathogen was exposed to that concentration of chlorine. Higher Ct factors indicate relatively higher resistance to chlorine, while lower Ct factors indicate relatively low resistance to chlorine. The Ct factors shown in the table were calculated from data in peer-reviewed research articles (references included).  The efficacy of disinfection using chlorine is dependent not only on the pathogen itself, but also on the pH and temperature of the water. 

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