Water comprises an estimated 50 percent of a women's body and 60 percent of a man's body. You can survive weeks without food, but only 5 to 7 days without water, because so many of your bodily functions rely on it. You lose water daily, through urine, sweat and respiration. When you don't drink enough water to replace lost fluids, your body starts to suffer.
Water to Prevent Dehydration
You start to feel thirsty when your water loss is at 1 percent. Signs of dehydration include dry mouth, fatigue, no urine output or dark yellow urine, no tears and sunken eyes. Your blood pressure might be low and your skin will lose elasticity. Water is also used in the delivery of oxygen. Without enough water, the blood flow to your tissues will be reduced. Severe dehydration can cause shock, coma and even death.
Water for Your Muscles, Joints and Temperature
When your body's water is reduced by 5 percent, your muscle strength and endurance suffer. Water lubricates your joints, keeping your movements smooth and preventing stiffness. It is an electrolyte necessary for transmitting nerve impulses that tell your muscles to contract. Water is also involved in the delivery of oxygen to your muscles. When you exercise, especially in warm conditions, drink plenty of water to keep your muscles functioning properly and to stay cool. Water allows you to sweat, and when sweat evaporates, your bodily temperature stays normal.
Water for Your Immune System
Your mouth and eyes are moist to prevent bacteria and other foreign substances from entering. Water keeps these areas wet to wash away dirt and grime. You should drink plenty of water to enhance your immune system, according to the article, ""Steer Clear of the Cold: Foods That Boost Your Immune System," by Heather Bauer published on the website of U.S. News & World Report. Urine is mostly water and urine removes waste from your body. Your urine output is severely depleted without enough water, which causes waste to build up, leaving you feeling ill.
Water for Eliminating Solid Waste
Water is needed to digest foods in your gastrointestinal tract. As food passes through your large intestine, your colon absorbs water to form stool. If the colon is not contracting well, it will absorb too much water causing constipation. Not drinking enough water is one of the most common causes of constipation, according to the Ohio State University Wexner Medical Center. Constipation may lead to hemorrhoids and rectal bleeding.