In 1908, Americans starting adding chlorine to drinking water to kill
bacteria and viruses that cause serious diseases like typhoid, cholera,
polio and hepatitis. In the U.S. today, all public water from surface
sources (rivers, streams and lakes) is chlorinated.
Chlorine is a highly reactive chemical, which is one reason why it
makes such a good disinfectant even in parts-per-million
concentrations. However, in addition to killing germs, chlorine reacts
with organic substances found naturally in drinking water (humic acids,
for example), and causes the formation of a class of chemical compounds
called trihalomethanes (or THMs). Some trihalomethanes have long,
obscure names like bromodichloromethane (a carcinogen in rodents),
dibromochloromethane, dichloroethylene, and dichloroethane, but some
are better known, such as chloroform, benzene, carbon tetrachloride,
and toluene, all of which are known or suspected carcinogens.
In 1974 Robert Harris, a scientist then working for the Environmental
Defense Fund (a traditional environmental group) published a report
showing a statistical link between cancer-causing substances in
drinking water and cancer incidence among humans in New Orleans, LA.
When Harris's report hit the newspapers, it created an uproar. Harris
was pilloried, as Rachel Carson had been 12 years earlier for
publishing Silent Spring. The water suppliers of America, municipal
officials, and many Right Thinking public health scientists went
berserk. "Absurd!" they said. "Hair-brained!" "Probably a communist!"
According to the conventional wisdom, chlorinating water was good for
people, not bad, and it was "irresponsible" to suggest otherwise.
There are people today who still believe Dr. Harris was wrong, just as
there are people who believe there is no connection between smoking and
illness. The Tobacco Institute, for example, still insists tobacco is
harmless, and the American Cancer Society, for example, does not even
list chemicals in our drinking water as a cause of cancer.
Between 1974 and today, at least 18 studies have appeared in the
literature linking carcinogens in drinking water to human cancers. Now
a massive new study has been reported in the JOURNAL OF THE NATIONAL
CANCER INSTITUTE, based on analysis of the water consumption habits of
2805 white men and women who have bladder cancer, compared to 5258
white men and women (matched for age, sex, and geographic area) who do
not have bladder cancer. The study drew subjects from 10 geographical
regions: Atlanta, Detroit, New Orleans, San Francisco, and Seattle,
plus the states of Connecticut, Iowa, New Jersey, New Mexico and Utah.
Trained interviewers administered a standardized questionnaire to
subjects (and controls) in their homes. Questionnaire items elicited a
life history including lifetime use of artificial sweeteners and
tobacco products, coffee consumption, use of hair dyes, a lifetime
occupational history, and a history of relevant medical conditions.
In a separate survey, trained data collectors analyzed records from,
and conducted interviews with managers at 1102 water companies in the
10 geographical areas the study covers (plus New York City and Chicago,
because so many subjects had lived in those places at one time or
another). Water samples were also collected from every water supplier,
and analyzed for trihalomethanes.
People use tap water for coffee, tea, reconstituted juice, soup, and
plain drinking water, as well as for cooking. (Beer and soft drinks are
customarily deionized and charcoal filtered, removing most chlorine
byproducts and other contaminants.) The average water intake among men
in the study was 2 liters per person per day, 1.4 liters of it from tap
water. Women drank, on average, 1.7 liters of water per day, 1.35
liters of it from tap water. The study revealed that those who drank 8
cups of chlorinated tap water for 40 to 59 years had a 40% greater risk
of bladder cancer than those who drank less tap water or who drank
unchlorinated water. People who drank the most tap water for 60 years
had an 80% greater risk of bladder cancer.
The effect was most pronounced among non-smokers. The researchers
speculated that the effect of smoking (which does cause bladder cancer,
as well as lung cancer and several other cancers) overwhelmed the
effect of chlorinated water among smokers. Among non-smokers who drank
chlorinated water for 60 years, the risk of bladder cancer was
The authors of the report emphasized that cigarette smoking and
occupational exposure to carcinogens are the main causes of bladder
cancer. Bladder cancer is diagnosed in 33,000 men and 12,400 women in
the U.S. each year. Among men, 70% of this is caused by cigarette
smoking and occupational exposure, the authors believe, and among women
40% comes from these causes.
Still trihalomethanes in drinking water appear to be a significant
contributor to the nation's total bladder cancer problem. Among the
subjects in the present study, 12% of the bladder cancer (336 cases)
could be explained by chlorinated water, the authors calculate. Among
nonsmokers, 27% of the bladder cancers are explained by chlorinated
Dr. Harris and many other scientists have said for a long time that we
should consider changing our method of disinfecting drinking water.
Europeans do not chlorinate their water because they do not like the
taste it gives to the water; instead, they bubble ozone through their
water, which kills germs but does not affect the taste. It also does
not create cancercausing trihalomethanes.
Two conclusions: Chlorinating our drinking water solves some problems
but creates others. We should switch to ozone treatment, abandoning
chlorine. Second, this study gives powerful new evidence that
chlorinated chemicals cause human cancers. Their industrial use should
For a free copy of this important study, contact Dr. Kenneth Cantor,
Landow Building, Room 3C08, National Institutes of Health, Bethesda, MD
20892; phone (301) 496-1691. Ask for a reprint of "Bladder Cancer,
Drinking Water Source, and Tap Water Consumption: A Case-Control
Study," JOURNAL OF THE NATIONAL CANCER INSTITUTE, Vol. 79, No. 6 (Dec.,
1987), pgs. 1269-1279. Footnotes 8 through 25 provide citations to 18
separate studies linking trihalomethanes to various cancers. Your local
librarian can help you track down copies of the 18 studies.
Descriptor terms: chlorination; chlorine; water; drinking water;
cancer; bladder cancer; risk assessment; ozone; trihalomethanes;
carcinogens; robert harris; edf; la; rachel carson; tobacco; american
cancer society; ga; mi; la; ca; wa; ct; ia; nj; nm; ut; opinion
surveys; health; health statistics; studies; findings;