Are Showers Detrimental to Your Health?

Recent research has shown that our exposure to trihalomethanes and other byproducts of water chlorination is much higher that previously thought(1,2,3). As a matter of fact, it is now clear that the lifetime risk of developing cancer from daily exposure to tap water is at least 20 in 100,000 person-years and may be as high as 100 in 100,000(4).

These risk factors are significant. For instance, the lifetime risk of developing leukemia from exposure to x-rays is estimated to be about 9 per 100,000 and that of developing breast cancer from x-ray exposure at about 50 per 100,000(5). Even the lifetime risk of developing Hodgkin's disease, a not uncommon form of cancer, is only 3 to 5 times greater than the risk of developing cancer from exposure to chlorinated drinking water(6).

The Environmental Protection Agency (EPA) is responsible for setting standards for acceptable levels of contaminants in drinking water. Their standard for chloroform, the most common trihalomethane in chlorinated water, is 100 parts per billion or 100 micrograms per liter of water. The EPA estimates that this level of contamination results in an added lifetime cancer risk of about 2 per 100,000 person-years. The EPA considers a cancer risk of 1 per million acceptable and a risk of 10 per 100,000 unacceptable(4).

The EPA bases its calculation of lifetime cancer risk on the assumption that the average person consumes about two liters per day of drinking water. Many researchers take issue with this assumption. A team from the Boston University School of Public Health believes that the cancer risk from chlorinated water may be 10 to 50 times higher than the EPA estimate(4). The reason for the discrepancy is that the EPA considers the actual ingestion of drinking water as being the only source of trihalomethanes.

It is, however, clear that we take in much more chloroform from bathing, showering, and doing the laundry than we do from actually drinking chlorinated water. Some studies have shown that the amount of chloroform that we absorb from a daily shower by inhalation and skin absorption is at least equal to the amount absorbed from drinking water and may be as much as 6 times higher(4). The cancer causing potential of inhaled chloroform is estimated to be about 20 times greater than the danger from ingested chloroform but may be as much as 75 times greater(4). What all this adds up to is that the danger of developing cancer from exposure to chlorinated drinking water is much greater than the authorities would like us to believe.

Evidence of this danger is now accumulating. As early as 1987 researchers at the National Cancer Institute reported that people who drank chlorinated water were twice as likely to develop bladder cancer than were people drinking non-chlorinated water(7). More recently, researchers at the New Jersey Department of Health reported that mothers who had been drinking water with a high level of trihalomethanes were more likely to give birth to babies with low birth weight and various birth defects(8). Researchers at the University of Arizona reported in 1990 that children whose parents had been exposed to drinking water contaminated with trichloroethylene were three times more likely to be born with congenital heart disease than were children whose parents had not been exposed to the contaminated water(9).

In conclusion, the risk of developing cancer from exposure to chlorinated water is significant. The EPA is vastly under-estimating this risk and their allowable chloroform content of municipal water of 100 parts per billion is too high. Not only is the limit too high, but there are many indications that it may not be adhered to. In 1982 alone there were over 70,000 violations of drinking water standards by municipal systems in the United States(11).