Chlorinated Water: Risks and Benefits

Chlorinated drinking water offers tremendous health benefits. Since chlorination was introduced in 1908 as a disinfectant for drinking water, the incidence of water-borne infectious diseases -- typhoid, cholera, polio and hepatitis, for example -- has dropped dramatically.

Concern about chlorination arose in the 1970s when scientists discovered that byproducts formed in the process of disinfecting water with chlorine caused cancer in laboratory animals. More recent population-based studies consistently found an increased risk of bladder and rectal cancer in humans who drink chlorinated water, noting a 21 percent increase in bladder cancer and a 38 percent increase in rectal cancer. (Researchers found no increased risk of brain, breast, colon, colorectal, esophageal, kidney, liver, lung or pancreatic cancer.) Before you eschew your public water supply, it's critically important to put these risks into perspective.

First, let's look at how these increases translate into numbers of people affected. According to the American Cancer Society (ACS), there are approximately 45,000 new cases of rectal cancer each year. Just 18 percent, or 8,100 cases are associated with drinking chlorinated water. The ACS estimates that there are 51,000 new cases of bladder cancer each year, with nine percent, or 4,644 attributable to chlorinated water. In contrast, say experts at the National Cancer Institute (NCI), the more significant causes of bladder cancer are cigarette smoking and occupational exposure, responsible for 70 percent of such cancers in men and 40 percent in women.

The most critical perspective, however, lies in considering the consequences of not chlorinating water. The World Health Organization estimates that 25,000 people die each day from diseases carried by inadequately sanitized water. In a year, that's 9.1 minion deaths. The risk of death from not chlorinating water, then, is of gargantuan proportions when compared with the chances of contracting cancer from drinking chlorinated water. One must also bear in mind that although contracting cancer may be devastating, many cancers -- including rectal and bladder cancers -- are treatable or even curable.

Finally, advises the NCI, it is still not clear which compounds in chlorinated water are responsible for the cancer association. In fact, it may not be the chlorine or chlorination byproducts causing the excess cancers. As with any population-based study, finding an association between some factor -- such as chlorinated water -- and increased disease -- in this case rectal and bladder cancers -- does not necessarily mean that the factor is responsible. Chlorination may only serve as a marker for some other aspect of drinking water quality or an associated geographic or demographic variable that causes the cancers.

Article copyright American Council on Science and Health, Inc.


By Kristine Napier

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