Over the last century, many North American cities have been adding chlorine to their public drinking systems, to successfully combat life-threatening diseases such as cholera and typhoid fever.

The Truth About Chlorine By-Products

Chemical reactions caused by chlorine, mixing with decaying organic matter, is known to produce several chemical by-products, the most consequential being trihalomethanes (THMs). Recent studies have shown that increased exposure to THMs have caused cancer in lab rats. In humans, long-term exposure to THMs can increase the likely-hood for developing certain types of cancer, namely bladder and colon cancer. Pregnant women are also at an increased risk to miscarry.

"Cancer risk among people drinking chlorinated water is 93% higher than among those whose water does not contain chlorine." — U.S. Council of Environmental Quality