Decay of Free Residual Chlorine in Drinking Water at the Point of Use

Dear Editor-in-ChiefDisinfected water at the water treatment plant may be polluted again when the water is being transported. Hence, the water should be protected against the possible pollutions by keeping the dis- infectant residues in the transportation line. If chlorine is selected as the disinfectant, it will be added to the water in a way that its residue re- mains in the line so as to prevent any unpredicted pollution. The term free residual chlorine (FRC) is given to each one of the (HClO), (OCl-), Cl- (g) compounds .Due to the following reasons it is better to diminish or removal the concentration of residual chlorine at the point of use.I. Recent studies show the chlorine in treated water is dangerous to human health and can cause allergic symptoms ranging from skin rash to intestinal symptoms to arthri- tis. Chlorine in water destroys protective lactic acid bacteria lining the colon, which cooperates and strengthen mucosal im- mune response against foreign pathogens at the intestine (1). On the other hand, an epidemiological study entitled "chlorina- tion water hardness and serum cholesterol in forty-six Wisconsin communities", demonstrated that serum cholesterol and low density lipoprotein cholesterol levels are significantly higher in chlorinated communities than in non-chlorinated com- munities (2). In some cases, patients are prevented to consume water that contains FRC.II. People usually use tap water for daily using, often disinfected by chlorine. Disinfection by-product such as Trihalomethanes (THMs) are formed in the preparation of many foods and drinks, by reaction of FRC with organic compounds in foods and drinks (3).So, it is better that before preparing food and drink, the chlorine is removed from water.III. FRC prevents to microbial contamination in water distribution system, but when was swallowed, its disinfection effect is un- important and is considered an additive. So, it is better to remove FRC from drink- ing water.IV. The concentration of free residual chlorine at the beginning of water distribution line is higher than that in the rest of the line. In fact, those who live in the vicinity of a water treatment plant receive more FRC in their water (4). It seems that the better way to deal with FRC in the distribution line is to remove it from the delivery path before the water is being consumed by people. In addition, due to the public awareness about the formation of hazard- ous by-products in water, people are in- creasingly approaching to the consump- tion of non-chlorinated water; further- more, increasing numbers of people are using water treatment devices in their homes to minimize the FRC concentra- tion present in water.For decay of chlorine there are two methods: 1- Storage of the samples at ambience 2- Storage of the samples in refrigerator. Results indicated that if water samples contain FRC (0.2-0.8mg/l) are maintained in ambience and refrigerator, after 24 hr, FRC will decrease by 62% and 51% respec- tively. …