researchers have found an increased risk of bladder cancer due to exposure to chlorinated water through drinking, swimming and bathing. The study was published online in the January 15, 2006, issue of American Journal of Epidemiology. The study found that exposure also occurs through inhalation and dermal absorption of trihalomethanes (thms) during such activities. thms are substances formed when natural organic material, such as the decaying vegetation commonly found in lakes and reservoirs, reacts with chlorine used to treat water. The most common thm is chloroform