Chlorine and ozone have served communities for nearly a century. 100 years ago ozone was too expensive and the ozone generation equipment not very reliable. At that time chlorine was cheap and its side effects unknown. Yet, because of chlorine's bad taste, and because of its terrible reputation as a WWI poison gas, after WWII ozone was already favored by many European cities. Today technology has made ozone generators relatively inexpensive and reliable.
It has been concluded in many studies that heart disease, cancer, and asthma are directly linked to the disinfectant by-products called TRIHALOMETHANES (THMs) and Halo-Acetic Acids. As 1000s of kinds of organic molecules may be present in water, there are also 1000s of Chloro-organics THM by-products formed when these organics react with chlorine. Each of them ever tested shows carcinogenic effects. The ultimate choice is Ozone.