Tap water supplied by municipalities for drinking purposes may get contaminated by toxic chemicals (organic & inorganic), living organisms, solid particulates and radioactive substances. It might contain toxic industrial wastes, chlorine by-products, fluoride, lead & other heavy metals that can cause cancer by damaging the DNA. Similarly, the groundwater may get contaminated by alpha particles released from natural radionuclides (such as Uranium, Radium and Radon) and human made radionuclides, which can cause cancer.
Chlorine is commonly used to kill harmful bacteria in the drinking water such as Shigella, Salmonella and Vibrio cholera. Chlorination of water can lead to formation of various cancer-causing compounds in the drinking water. When chlorine reacts with organic matter present in the water, certain toxic and carcinogenic compounds known as trihalomethanes are produced, which include Chloroform and Trichloroethylene. Chloroform (earlier used as an anaesthetic agent), has already been banned since 1976, due to its carcinogenic effect. It has been observed that the prolonged use of chlorinated water can lead to genesis of cancers of the rectum and the bladder. When chlorine interacts with the humus in water (that is produced by decaying plants in water), it produces two chlorinated acids known as MX and DCA. Both of these chlorinated acids promote the growth of cancer and possess mutagenic activity. DCA is known to cause cancer of the liver. A Norwegian study published in 1992 in the “International Journal of Epidemiology” revealed that the incidence of colorectal cancer increases 30 percent due to consumption of chlorinated water. Inhalation of chlorine is even more dangerous than drinking the chlorinated water. According to a report published in the International Health News, the amount of chloroform inhaled or absorbed through the skin during a shower is 6 times higher than that absorbed from the chlorinated drinking water in a day. It has been observed that about 70 percent of toxins found in water enter into the body through skin during bath & shower.
Fluoride is another highly toxic and carcinogenic compound that has been added to the public drinking water and toothpaste since the 1950s, with the aim to protect teeth against formation of cavities. It has been observed that fluoride has carcinogenic effects in concentrations as low as 1ppm. Fluorine (a component of fluoride) slows down the mechanism of natural DNA repair. Fluoridated water causes bone and skin cancers.