Humans need to drink water to survive. Your body is approximately 60 percent water, your brain is 70 percent water, and your lungs are nearly 90 percent water. Each day, your body must replace 2.4 liters -- or about 2.5 quarts of water -- through ingested liquid and foods.
Body Uses Water
Your body uses water in many ways. Water cushions and lubricates joints; nourishes and protects the brain, spinal cord and other tissues; keeps the body's temperature normal; and helps remove waste through perspiration, bowel movements and urination. Humans are composed mostly of water, which is not surprising when you consider that humans descended from single-cell organisms that originated in the oceans millions of years ago.
Lack of Water
Water is more important for your body's survival than food. You can live without water for approximately one week, but you can survive without food for more than a month. Lack of water, or dehydration, reduces the amount of blood in your body, forcing your heart to pump harder in order to deliver oxygen-bearing cells to your muscles. In the early stages of dehydration, you can become dizzy, irritable and experience headaches. As dehydration progresses, you become clumsy and exhausted. Your eyesight fades. In the last stages of dehydration, you may feel nauseous and begin vomiting. Without water, you will enter a coma and die.
Too Much Water
When you drink too much water, you can develop a condition known as hyponatremia, in which the excess water floods your body's cells, causing them to swell up. Your swollen brain cells then cause a wide range of symptoms, including a bad headache, nausea, cramps, mental confusion, convulsions, fatigue, coma and death. Hyponatremia has killed runners during marathons.
You may have been told that in order to be healthy, you must drink eight glasses of water each day, and each glass must contain 8 ounces of water. You may also have been told that only water will fulfill this requirement, not other liquids that contain either caffeine or alcohol. Both ideas appear to be myths, according to Dr. Heinz Valtin of the Dartmouth College Medical School. In a 2002 paper published in the "American Journal of Physiology," Dr. Valtin found no scientific evidence supporting consumption of eight glasses of water daily. He did find studies that suggested that caffeinated beverages and mild alcoholic drinks, such as beer, can contribute to the water needed by your body.
A British Broadcasting Corporation essay, "Why Do We Need Water?" notes that tea, coffee and fruit juices also count toward your liquid intake and recommends that healthy adults should drink between six and eight medium-sized glasses of fluid daily. People should drink more liquids if they are physically active or experiencing hot weather. The best way to determine if you are getting enough water is to look at the color of your urine. If it is a pale straw color, you are probably drinking enough. If it is dark yellow, you may need to drink more.
Credit By : Robin Elizabeth Margolis, Demand Media