Municipalities routinely began using chlorine to treat drinking water starting in 1908 with Jersey City, NJ. Its use has helped to virtually eliminate diseases like typhoid fever, cholera and dysentery in the US and other developed countries. Globally the World Health Organization (WHO) estimates that 3.4 million people in underdeveloped countries die every year from water-related diseases. Use of chlorine in water can produce an undesirable taste; therefore, many consumers prefer to remove it. Disinfection byproducts (DBPs) may also unintentionally form when chlorine and other disinfectants react with natural organic matter that is in the water. To reduce DBP formation, many municipalities are switching to monochloramine. Monochloramine treatment was first used in Ottawa, Ontario, Canada in 1916 and in Denver, CO in 1917. Use of monochloramine took a downturn during World War II due to ammonia shortages. Currently the US EPA estimates more than 30 percent of larger US municipalities use monochloramine. It’s a common misperception that activated carbon removes chlorine and monochloramine from water by adsorption. Understanding how activated carbon removes chlorine and monochloramine from water is critical to the design and operation of such systems. . . . .The addition of any of these to water will producehypochlorous acid (HOCl). This disassociates into hypochlorite ions (OCl-) to some degree. (The reaction is summarized below). Cl2 + H2O → HOCl + H+ + Cl– HOCl - → H+ + OCl+ The ratio of hypochlorous acid and hypochlorite ion in water is dependent upon pH level and, to a much lesser degree, water temperature. The ratio of hypochlorous acid and hypochlorite ion at various water pH and temperature is shown in Table 1.