Around 65 percent of weight of an average, healthy human body is accounted for by water. The exact figure depends on the build of the person. In a thin person it may as high as 70 percent, while in a plumb person it may be even less than 55 percent. Each individual is finely tuned to his normal requirements of water. When the amount of water in the body goes down even slightly (1 or 2 percent), this situation is indicated by responses such as thirst. A greater drop, of say 5 percent, a cause to shrink, the mouth and tongue to go dry, and even hallucination. A drop of 15 percent can cause death by dehydration. Intake of water in excess of need is equally bad. It can cause a series of mental and nervous disorders and finally death.
Within the body, water performs a variety of functions. It lubricated the joints between bones to prevent them from rubbing against each other. Similarly, it forms a sheath around soft tissues to prevent them from sticking. Vital organs, like the brain and the heart, are enclosed in a protective fluid made up largely of water. Water protects the internal chemical processes of the body from violent fluctuations in pressure, acidity and chemical composition.
Water is the vital communication link between various parts of the body. It serves as a carrier of food and waste, oxygen and carbon dioxide. It is the medium through which heat energy is circulated rapidly around the body by the bloodstream of which it forms a very substantial part. The cooling action of water produced by the evaporation of sweat (largely water) from the skin keeps the heat of metabolism- the process by which food is converted into energy- within tolerable limits. Water aids the passage of molecules of nutrients through the walls of cells. It plays a very important role in the digestion of food. It transports wastes from body by perspiration, urine and digestive wastes (excreta).
Because of these complex functions of water in the body, its own balance must be precisely regulated in terms of not only quantity but also quality. In the natural course of the thing the body system is programmed for such regulation. But when an abnormality of any kind gets introduced into the system, a disruption of one or more of these natural processes can occur. Consuming water-containing contaminants such as Bacteria, Viruses and Parasitic Protozoan, Lead, Copper, Nitrate, Nitrite, Arsenic, Benzene, Gasoline, pesticides and herbicides above the maximum contaminant level set by the regulations over a period of time could cause chronic or acute health problems. Of particular concern are children, older persons, or those whose immune systems have deficiencies or are not fully developed. So, safe drinking water is the must. So it is really very necessary to make sure the water we were taking is the safe one.