THM or Trihalomethanes are a by-product of the chlorination of naturally occurring water supplies. Chlorination has made water supplies in North America safe from illness causing bacteria, parasites, and viruses. The vast majority of US and Canadian citizens living in urban areas are fortunate that chlorination systems are used, and have virtually eliminated the risk of waterborne diseases such as dysentery, cholera, and typhoid. However, studies conducted over the last few decades have illuminated some possible risks from consuming water that has been treated with chlorine. Most of the risks are associated with a chlorination byproduct called Trihalomethane or THM for short. 

THM is produced when chlorine is added to natural surface waters (lakes, rivers, streams) or ground waters (springs, wells). Naturally occurring organics in the water react with the chlorine to form THM. A U.S. Environmental Protection Agency survey discovered that THM is present in almost all chlorinated water supplies.

So what's the big deal?

• Scientific studies have linked THM to an increased risk of cancer

• Scientific studies have linked THM to an increased risk of miscarriage

• It is suspected that THM may be linked to heart, lung, kidney, liver, and central nervous system damage

Due mainly to the concerns about cancer, the US Environmental Agency (EPA) has limited the amount of THM to 80 parts per billion (ppb) in municipal water supplies. Reverse Osmosis and Carbon Water Filters systems greatly reduce the amount of THM found in drinking water.