What solution in the USA is most commonly used to purify swimming pool water?

Chlorine is the most widely used sanitation method, but is becoming less desirable because of the harmful byproducts it produces and its difficulty inactivating cryptosporidium. Chlorine is a relatively strong oxidizer and bactericide, but it creates chloramines and trihalomethanes (THMs), which cause irritation to the eyes, skin, throat and lungs.Chlorine has been used for applications, such as the deactivation of pathogens in drinking water, swimming pool water and wastewater, for the disinfection of household areas and for textile bleaching, for more than two hundred years.