Most of us take for granted that the water flowing from our tap is clean and pure. We compare our tap water with the standards of much of the world and we reassure ourselves that the water in our drinking glass is safe. But we should be asking an important question: “safe” and “pure” compared to what?

The practice of purifying our drinking water with chlorine was pioneered by the military a century ago. It began to be commonplace in the U.S. in the 1930’s and was widespread by World War II. Chlorination has been a major boon to human health: the spread of water-borne diseases that still claims millions of lives around the world soon became a thing of the past in the developed world. That, as they say, is the good news.

But remember Dr. Mixon's first rule:  “Anything strong enough to help is strong enough to hurt!” That applies to chlorination of water in a surprising way. Chlorination very effectively kills bacteria, parasites, and viruses. But as they are destroyed, these organisms and their component parts do not simply vanish. The chlorine rips them apart and transforms the basic molecules of their bodies into a series of compounds referred to as “halomethanes,” or chlorination sterilization byproducts (sometimes referred to as “disinfection byproducts”).