The human body is composed of approximately 70 percent water. In fact, the body's water supply is responsible for and involved in nearly every bodily process, including digestion, absorption, circulation, and excretion. Water is also the primary transporter of nutrients throughout the body and so is necessary for all building functions in the body. Water helps maintain normal body temperature and is essential for carrying waste material out of the body.
Most people assume that when they turn on their kitchen tap, they are getting clean, safe, healthy drinking water. Unfortunately, this is often not the case. Regardless of the original source of tap water, it is vulnerable to a number of different types of impurities. A study conducted by the Natural Resources Defense Council found that 18,500 of the nation's water systems (serving some 45 million Americans) violated safe drinking water laws at some point during 1994. The council's report blamed contaminated water for some 900,000 illnesses a year, including 100 deaths. Even if the levels of individual substances in water are well within "allowable" limits, the total of all contaminants present: may still be harmful to your health.
Long considered a problem limited to poor, developing countries, the presence of bacteria and parasites in drinking water especially a parasite called cryptosporidium is becoming a serious problem in the United States today. In 1993, the residents of one of Wisconsin's largest cities were forced to boil their tap water after it was discovered to contain “unacceptable” levels of cryptosporidium, most likely from agricultural run-off. This outbreak was suspected of causing six deaths in the area. The same organism has created controversy over the safety of the water in New York City; many people with weakened immune systems have charged that cryptosporidium in the city water has made them sick, even though local officials insist that the water is safe to drink. For people with HIV or AIDS, cryptosporidium can be lethal. The chlorine added to water to kill bacteria is not effective at killing these parasites.