Drinking Water and Chlorine Odor

How would you describe your tap water? A rich bouquet of earthy flavors? Sulfurous with a hint of chlorine? Or simply divine? The aesthetic properties of your tap water depend upon your local natural water supply source, how your water is treated, and how it is delivered to you.

In the case of private well water that undergoes no treatment at all, taste and odor are simply a function of the presence of naturally occurring minerals and organic matter in the locally tapped groundwater. Municipal treatment, however, adds another level of “complexity” for the palate.

According to the American Water Works Association (AWWA), “ultra-treated” water is disagreeable. Distilled water, for example, which is pure water with no dissolved components, tastes flat, bitter, and astringent. (You would know this if you have ever tasted distilled water sold for steam ironing.) That’s because our mouths are accustomed to the pH and mineral content of our saliva, which are quite different from those of distilled water.

A refreshing glass of drinking water requires certain chemicals be present in combination, such as calcium and bicarbonates. And a drink of water that originated from a municipal treatment plant probably made contact with chlorine when it was added to destroy waterborne germs, such as e. coli 0157 H7 and norovirus, which are capable of spreading disease. Chlorine disinfectants play an essential role in maintaining the public health, but they can introduce an unpleasant odor or taste to drinking water.

Smells Like Chlorine

The chlorine odor of tap water can be traced to the chlorine “residual,” a low level of chlorine maintained in water to guard against bacteria, viruses and parasites, which may be in water as it flows from the treatment plant to points of use. In the US, even treatment plants that use non-chlorine disinfection technologies are required to add chlorine to the water before it flows into the distribution system. The chlorine residual acts like a “body guard” for water in transit. As long as there is a residual level of chlorine, the consumer is reasonably protected from harmful microorganisms.

According to the AWWA, if the chlorine residual level is sufficient without being excessive, water will not smell like chlorine. Yet, sensitivity to the odor of chlorine varies among consumers. The US Environmental Protection Agency (EPA) requires treatment facilities to maintain a chlorine residual level that is chemically detectable but no greater than 4 mg/l. Four milligrams per liter is the “Maximum Residual Disinfectant Level” for chlorine, and it is the level below which there are no known or expected risks to health from exposure to the disinfectant.

Most people can sense a chlorine residual around 1 mg/l. If your water smells strongly of chlorine, it is possible that your treatment facility conveys water over a long distance, requiring heavy chlorination to maintain a chlorine residual throughout the system. (The chlorine residual also may be raised by treatment facilities during warm weather when chlorine dissipates readily from water.) AWWA notes that this can be remedied by systems reducing chlorine added at the point of entry and installing booster chlorination systems in the distribution line. The consumer also has practical options (see text box).

Consumer Confidence Report

Do you have a question about your drinking water quality? If your home is served by a community drinking water system, you should receive a consumer confidence report (CCR) from your water supplier each year by July 1. A CCR provides a general overview of the water quality delivered. This EPA website contains links to some drinking water systems reports and a Frequent Questions section. If you still have questions, contact your water supplier.

Linda Golodner is President Emeritus of the National Consumers League and Vice Chair of the Water Quality & Health Council.