Does chlorine in drinking water increase the risk of Cancer?

THE CLAIM

Chlorine in drinking water can increase the risk of cancer

THE FACTS

Companies that sell water filters often claim that the chlorine in most tap water causes cancer. Is it true? Scientists say chlorination can produce at least one group of chemical byproducts, trihalomethanes, that are considered carcinogenic. But studies over the years have differed on whether levels of these compounds in tap water adversely affect health.

Some studies have found a link to cancer, others have not. The most reliable findings may be those of meta-analyses, large studies that pool results of many smaller ones. Three such meta-analyses in 1992, 2003 and 2004 linked long-term consumption of chlorinated water to small increases in the rates of bladder cancer, particularly in men. Several agencies, including the World Health Organization, say the evidence is weak and point out that any risk from chlorine byproducts is tiny compared with risks associated with non-chlorinated water. Many countries that have relaxed chlorination standards have seen outbreaks of cholera and other diseases.

THE BOTTOM LINE

Some studies have found byproducts of chlorination associated with a slight increase in cancer risk, but the findings are disputed by major health organizations.