Which type of pathogens is chlorine ineffective at disinfecting?

Chlorine is widely recognized for its disinfecting capabilities and is particularly effective against many types of pathogens, including bacteria, viruses, and fungi. However, it is significantly less effective against certain parasites. Specifically, chlorine does not effectively kill cysts of protozoan parasites such as Giardia lamblia and Cryptosporidium. These organisms can withstand chlorine residuals commonly found in treated water, making chlorine inadequate as a sole disinfection method for water contaminated with these parasites.

This understanding emphasizes the necessity for specific treatments or alternative disinfectants when dealing with waterborne diseases caused by certain parasites, highlighting the limitations of chlorine as a disinfectant in those scenarios.