Factors that affect how much water an individual needs include age, physical activity and environmental temperature. The elderly and young children are more susceptible to dehydration. Although the government claims our water systems are safe, some people are concerned about levels of chlorine or other contaminants in water. Simple activated charcoal filters will remove most of these substances. But if you keep water around for days, say in a pitcher in the refrigerator, you might be better off with chlorinated water.
Chlorine is added to kill bacteria in water pipes.
There have been a few highly publicized failures of municipal disinfection in recent years. The biggest was during 1993 in Milwaukee, Wisconsin where the parasite Cryptosporidium killed more than 100 people and caused hundreds of thousands of illnesses. This parasite is not killed by chlorine and must be filtered out. New EPA standards will improve filtration of all big water supplies. People with weakened immune systems must avoid this microorganism.