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.