Health Effects of Chlorine in Drinking Water

Until recently, concerns about drinking water focused on eliminating pathogens (bacteria). Chlorination of drinking water is a major factor in the reduction of mortality rates associated with water borne pathogens. The use of chlorine was believed to be safe and was thought to make any municipal water supply as pure as mountain spring water, that chlorination destroyed all microbial life leaving no trace of it afterwards. Though chlorine does reduce the risk of infectious disease, it is now thought to account for a substantial portion of the cancer risk associated with drinking water.

Chlorine, a halogen, is a corrosive, poisonous, greenish-yellow gas with a suffocating odour. Chlorine is changed to liquid form by compressing the gas; the resulting liquid is then used for mixing in the water to destroy bacteria. But this chlorine ends up reacting with organic matter such as leaves, twigs, or agricultural chemicals in the water and forms dangerous, carcinogenic trihalomethanes. Concerns about effects of chlorination by-products in water have resulted in numerous epidemiological studies and was found that people who regularly drink tap water containing high levels of chlorine by-products have a greater risk of developing bladder and rectal cancers than people who drink unchlorinated water. These studies have estimated that about 9 percent of all bladder cancer and 18 percent of all rectal cancer cases are associated with long-term consumption of chlorine by-products (trihalomethanes). These products can also cause artherosclerosis and its inevitable result, the heart attack or stroke.

Point of use water treatment systems are effective in reducing risks associated with chlorination of water. Use of activated carbon filters is the simplest remedy.