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.
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 colour of your urine. If it is a pale straw colour, you are probably drinking enough. If it is dark yellow, you may need to drink more.