Known also as H2O, water is made up of two parts hydrogen and one part oxygen; water makes up about 50 to 65 percent of the weight of an average-sized adult. This means that the adult body contains about 45 liters of water, 30 liters of which circulate within the cells, three liters of which circulate as blood plasma, and 12 liters of which make up the interstitial fluid. Humans can survive only a couple of days without water. A loss of 5 to 10 percent causes major dehydration, and a 15 or 20 percent loss usually causes death.
Why is water so necessary for survival? Well, it's used in just about every body function. It's necessary for the digestion, absorption, and transport of nutrients. It acts as a solvent to dilute and excrete body waste, it's the medium for many chemical processes, and it helps regulate and maintain body temperature. Water builds body tissues, makes body fluids possible, keeps skin soft and supple, and helps lubricate organs and joints.
Watch: Glass of Ice Water
It is suggested that adults consume from six to eight glasses of water a day, which can come from plain water as well as coffee, tea, soft drinks, and juice. Water can also come from fruits and vegetables, which are 70 to 95 percent water. On hot days, the body requires more water, as it does during exercise or when the body is experiencing illness. In general, humans need as much water per day as they excrete through urine, stool, lung vapor, or perspiration.
Can you drink too much water? You can, but it's not very common. When you drink more fluid than you need, the body responds by making more urine. But when you drink way more water than needed, water intoxication can occur, in which convulsions, coma, and even death can result.
You can learn more about the nutritional value of water by visiting this Water information resource, which is published by the U. S. Department of Agriculture.
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Water Nutritional Guide - H2O