As an alternative, some cities are switching to a form of water treatment called ozonation, which uses ozone gas to kill microorganisms. Ozonation, Europe's favorite method, doesn't produce trihalomethanes. The whole issue is the balancing. We don't want to cut back disinfection. If anything, we'd like to strengthen it.
Nobody knows how to do it.
In most U.S. water systems, the unwanted byproducts form when the chlorine reacts to decayed vegetation and other organic carbon in water. So, cities that take drinking water from lakes and rivers have a tougher time keeping the chlorine byproducts out of the tap than those that use clean groundwater. On bad days with a lot of debris in reservoirs, water suppliers try to switch to such alternate sources as wells. Or some combine chlorine with ammonia in a disinfection method called chloramination. The method isn't as potent as pure chlorination, but stops the production of unwanted trihalomethanes.