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Chlorine and bladder cancer.  January 2007.

The findings are the first to suggest that these chemicals can be harmful when they are inhaled or absorbed through the skin, as well as when they are ingested, Dr. Cristina M. Villanueva of the Municipal Institute of Medical Research in Barcelona, and colleagues note.

Chemicals, most commonly chlorine, used to disinfect water can produce by-products that have been tied to increased cancer risk, Villanueva and her team point out. The most prevalent chlorination by-products, chemicals called trihalomethanes (THM), can be absorbed into the body through the skin or by inhalation.
The disinfection of water bychlorination or, to a lesser extent, by chloramination, can produce a number of by-products due to the interaction of chlorine with naturally occurring organic substances in the water. Included in these by-products are the trihalomethanes (THMs).Those which have been of greatest interest are:  Chloroform, bromodichloromethane, Dibromochloromethane, tribromomethane.

To investigate lifetime THM exposure and bladder cancer risk, the researchers matched 1,219 men and women with bladder cancer to 1,271 control individuals who did not have the disease, surveying them about their exposure to chlorinated water via drinking water, swimming pools, showering and bathing. The researchers also analyzed the average water THM levels in the 123 municipalities included in the study.

People living in households with an average household water THM level of more than 49 micrograms per liter had double the bladder cancer risk of those living in households where water THM concentration was below 8 micrograms per liter, the researchers found. THM levels of about 50 micrograms per liter are common in industrialized societies, they note.

Study participants who drank chlorinated water were at 35% greater risk of bladder cancer than those who didn’t, while use of swimming pools boosted bladder cancer risk by 57%. And those who took longer showers or baths and lived in municipalities with higher THM levels were also at increased cancer risk.

When THM is absorbed through the skin or lungs, Villanueva and her team note, it may have a more powerful carcinogenic effect because it does not undergo detoxification via the liver.

“If confirmed elsewhere, this observation has significant public health implications in relation to preventing exposure to these water contaminants,” the researchers conclude.

PURPOSE:
The purpose of this study was to investigate the carcinogenic potential of chlorinated or chloraminated drinking water and of four organic trihalomethane byproducts of chlorination (chloroform, bromodichloromethane, chlorodibromomethane, and bromoform) in rats and mice.

RESULTS:
The trihalomethanes were carcinogenic in the liver, kidney, and/or intestine of rodents. There was equivocal evidence for carcinogenicity in female rats that received chlorinated or chloraminated drinking water; this evidence was based on a marginal increase in the incidence of mononuclear cell leukemia.

CONCLUSION:
These results suggest that organic by products of chlorination are the chemicals of greatest concern in assessment of the carcinogenic potential of chlorinated drinking water.

"The drinking of chlorinated water has finally been officially linked to an increased incidence of colon cancer. An epidemiologist at Oak Ridge Associated Universities completed a study of colon cancer victims and non-cancer patients and concluded that the drinking of chlorinated water for 15 years or more was conducive to a high rate of colon cancer." Health Freedom News, January/February 1987

"Long-term drinking of chlorinated water appears to increase a person's risk of developing bladder cancer as much as 80%," according to a study published in the Journal of the National Cancer Institute. Some 45,000 Americans are diagnosed every year with bladder cancer. St. Paul Dispatch & Pioneer Press, December 17, 1987

"Although concentrations of these carcinogens are low...it is precisely these low levels which cancer scientists believe are responsible for the majority of human cancers in the United States." Report Issued By The Environmental Defense Fund

"Chlorine itself is not believed to be the problem. Scientists suspect that the actual cause of the bladder cancers is a group of chemicals that form as result of reactions between the chlorine and natural substances and pollutants in the water." (organic matter such as leaves and twigs.)
Source :   St. Paul Dispatch & Pioneer Press, December 17, 1987

Protozoan parasites such as Cryptosporidia and Giardia lamblia, and viruses like hepatitis A and E, rotavirus, Norovirus, poliovirus and echovirus can be present in drinking water even when the water is chlorinated.
People can become extremely sick by swallowing a few protozoa since they rapidly reproduce once inside a host organism.
Cryptosporidium caused a cryptosporidiosis outbreak in Milwaukee in 1993 that resulted in over 400,000 cases of serious illness and 100 deaths.
Emerging Issues in Water and Infectious Disease, World Health Organization, 2003