CWQA Position Statement Drinking Water Chlorination & Point-of-Use Dechlorination in the Home The use of chlorine for more than 80 years has been the primary means of controlling health related micro-organisms in municipal water supplies and has had exceptionally positive results. To assure proper disinfection, a chlorine residual must be present in the water throughout the entire water distribution system; however, when chlorinated drinking water reaches the consumer’s tap, objectionable tastes, odours and by-products of chlorination can be reduced effectively and economically with home water quality improvement equipment that has been properly designed, applied and maintained.
Summary: Continuous application chlorine to disinfect public water began in 1908 in Chicago and Jersey City. Waterborne disease such as typhoid fever was prevalent then.2 Major cities were suffering 100 or more typhoid deaths a year per 100,000 persons.4 Within the next ten years, thousands of drinking water treatment plants initiated chlorine disinfection. The typhoid death rate fell simultaneously. The number of typhoid fever cases is now insignificant as a direct result of the widespread use of the combined process of chlorination and filtration in drinking water treatment. Proper chlorine disinfection remains, therefore, a most important and beneficial water treatment process. At the same time, however, chlorine reactions in drinking water can cause taste and odour problems. Delayed reactions with phenolic compounds in water, for example, result in intermediate chlorophenols which are highly odourous. Typical chlorophenolic tastes and odours can result in water that is unpalatable or otherwise unacceptable to many consumers. Chlorine can also react with humic and fulvic acid present in natural waters to form undesirable organic by-products.2 Trihalomethanes (THMs), for example, are such byproducts of chlorination. Government agencies have classified various THM compounds as either probable or possible human carcinogens. Government agencies "Drinking Water Regulations" established a Maximum Contaminant Level (MCL) of 0.10 milligrams per litre for THMs and a Maximum Contaminant Level Goal (MCLG) of zero. Finally, in the addition to the problem of taste, odour and by-products created by chlorination, residual chlorine has a deleterious effect on various other water treatment products and equipment commonly used in the home. For example, some ion-exchange resins used in demineralizers and water softeners, as well as some membranes used in reverse osmosis water treatment equipment, may be adversely affected by the presence of a residual chlorine in the water to be processed. Such products are used to control a variety of aesthetic and health related substances in home drinking water and as a result of prolonged exposure to traces of chlorine, the ability of these products to control the target substances will be reduced or eliminated. Consequently, dechlorination of water and removal of chlorination by-products at the point-of-use is often desirable and for the protection of home water treatment resins and membranes even necessary. The addition of chemical reducing agents such as sulphur dioxide, sodium sulphite and sodium bisulphite or prolonged storage in an open reservoir will remove chlorine from water.3 However, the most widely used effective and appropriate means of removing both chlorine and chlorine by-products from drinking water in the home is the use of properly designed, installed and maintained activated carbon filters, distillers or other correctly applied home water quality improvement equipment.
REFERENCES: 2. American Water Works Association, Water Quality and Treatment, A Handbook of Community Water SuoDlies. Fourth Edition, 1990, pp. 135-145 and 877-932. 3. Betz Handbook of Industrial Water Conditioning. Sixth Edition,1962, pp. 52-53. 4. McDermott, James J., "Federal Drinking Water Standards, Past, Present and Future Journal of Environmental Engineering Division. ASCE, Vol. 99, No. EE4, Proc Paper 9924, August 1973, pp. 469-478. |