Chlorine is effective at killing germs that make people sick. However, it is essential to monitor chlorine levels and allow them time to produce their intended benefits. The chemical can kill the majority of germs that cause recreational water illnesses in mere minutes but will take longer for parasites such as Cryptosporidium, which can survive for days even in water that has been properly disinfected. To ensure chlorine reaches its full germ-killing potential, keep your swimming pool free of debris and practice good hygiene before taking a dip.