A recent Scientific American column grossly overplays an unsubstantiated risk associated with drinking water chlorination. It overlooks the benefits of chlorine as an inexpensive and highly effective disinfectant and does not recognize that the regulatory limits for chlorine and disinfection byproducts were set following a thorough review of credible health data. The article blatantly promotes a particular water filter product, reading much like an advertisement yet raising serious questions about whether its “facts” received adequate editorial scrutiny. All in all, this is a curious piece to find in a journal with the credibility of Scientific American.

First, the article references the damaging effects of chlorine gas used in World War I and suggests its use in drinking water is equally as harmful. In fact, there is no link between the use of chlorine gas in World War I and the potential for “disinfection byproducts,” or “DBPs” to cause cancer.

The U.S. Environmental Protection Agency (EPA) requires treated tap water to have a detectable level of chlorine to help prevent contamination. The allowable chlorine levels in drinking water (up to 4 parts per million) pose “no known or expected health risk [including] an adequate margin of safety.” Only chlorine disinfectants can provide this “residual” protection all the way to consumers’ taps.

Second, a source quoted in the article says that researchers have linked chlorine in drinking water to higher incidences of bladder, rectal and breast cancer, but this link has not been proven. All chemical disinfectants combine with trace levels of natural organic matter present in drinking water to form low levels of disinfection by-products, or DBPs. The EPA, concerned that some of these chemicals, such as trihalomethanes (THMs), could be carcinogenic to humans, has set regulatory limits for DBPs. In other words, all drinking water that meets the EPA standards is safe for consumption. It is also important to understand that neither the EPA nor the International Agency for Cancer Research considers chlorine to be a carcinogen.

Finally, the “recent study” on breast cancer conducted in Hartford, Connecticut that is referenced in the article was actually published in 1992. This study (Falck et al.) examined pesticides like DDT and PCBs, which contain chlorine but have very different properties from chlorine used as a disinfectant or byproducts of water chlorination. Two major review articles by leading scientists also cast doubt about the link reported in the Connecticut study (Adami et al., 1995, and Ahlborg, et al., 1995).

The reality is that chlorine destroys microorganisms that can cause deadly waterborne diseases. Since 1908, when chlorine was first used on a large scale to purify U.S. drinking water, waterborne diseases, such as typhoid fever and cholera, have been virtually eradicated. But in developing nations where communities lack widespread access to safe drinking water, diseases associated with dirty water kill more than 25,000 people per day. Most of these are children under the age of five. As a result, international public health agencies, such as the World Health Organization, strongly caution:

The health risks from these byproducts at the levels at which they occur in drinking water are extremely small in comparison with the risks associated with inadequate disinfection. Thus, it is important that disinfection not be compromised in attempting to control byproducts.

While alternative disinfection methods are growing in popularity, they too have disadvantages. For example, ozone creates DBPs, many of which have not been studied for their potential effects to human health. Further, cities such as Las Vegas that are using ozone, are not completely chlorine-free. According to EPA requirements, they must still maintain a "residual" level of chlorine in treated water to prevent recontamination in the distribution system.

The next time you come across a story about the alleged negative health effects associated with chlorine disinfectant used in drinking water, remember that chlorine has been used safely and effectively for more than a century to provide healthy, clean drinking water. It is being rushed to earthquake-ravaged Haiti right now, where it is desperately needed to prevent waterborne disease outbreaks. Simply put, the real danger, when it comes to chlorine, is eliminating its use.

Please visit our website to learn more about the safety benefits of chlorinated water. You can also tell Scientific American to retract this unscientific column by sharing on Twitter RT @chlorine - @sciam Stand up for science – retract bogus claims about drinking water and chlorine!

(Chris J. Wiant, M.P.H., Ph.D., is president and CEO of the Caring for Colorado Foundation. He is also chair of the Water Quality & Health Council.)

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