Should I Be Concerned About the Chlorine in My Drinking Water?

Gina Solomon responds:

Chlorine itself is somewhat irritating to the skin and mucous membranes, so people with sensitive skin can have problems when they shower in chlorinated water. The real problem with chlorine, however, is that it chemically reacts with other organic material in the water to create disinfection by-products known as trihalomethanes, or THMs. The most familiar THM is chloroform, but there are many others. THMs have been linked to bladder cancer and to reproductive disorders including miscarriage. They are volatile and therefore can be inhaled in the shower or even when washing dishes. The EPA has taken some action in recent years, reducing allowable amounts of THMs in drinking water. In response, many water systems have switched to chloramine (which is basically bleach), and some forward-thinking systems have begun using an ultraviolet-light disinfection pretreatment. Chloramine is a concern as well, not only because it will kill your pet fish, but because it creates a variety of disinfection products that seem to be as bad as—or worse than—the THMs.  
 
The good news about these disinfection by-products is that they are readily removed by most carbon filters, including countertop filters such as those made by Brita. Since these chemicals are volatile, you can even remove them simply by letting water stand in a pitcher in the fridge or on the counter for a little while before drinking it. Boiling water (as when preparing tea or coffee) also eliminates these chemicals.  
 
If you are on a municipal water supply, ask for the water system's consumer confidence report, which should include testing results. This should come at least annually in your water bill anyway, and it's also usually posted on the utility's Web site. The legal maximum for THMs is 80 parts per billion (ppb), and the maximum for other disinfection by-products, known as haloacetic acids (HAA5), is 60 ppb. Ideally the numbers should be considerably lower than these. If the numbers are even close to these levels, consider using a carbon filter or filter pitcher.