Water is ranked second only to oxygen as essential for life. Your overall body weight is two-thirds water. A person can survive about two months without food, but only a few days without water.
Every system in your body depends on water to function. Water is essential to your body's temperature regulation, keeping it cool through perspiration. It flushes out toxins and wastes. Also, it's a major component to help blood carry nutrients and oxygen to and from all cells.
Water provides a moist environment for all body tissues. It is the major component of saliva and mucous which lubricates the membranes that line our digestive system beginning with the mouth. Mucous membranes in the nose and eyes function better when well hydrated. It cushions joints and protects tissues and organs like the brain from shock and damage.
Additionally, water helps you to maintain a healthy weight. It is hard to distinguish between hunger and thirst. If you feel hungry, drink some water first and then reassess your hunger status. Each day your body can lose 2-3 quarts of water through sweat, urination, excretion and breathing.
The body loses even more water if you exercise, live in hot or dry climates, consume high-fiber diets, and consume caffeine or alcohol. It is recommended to drink 8-10 cups of fluid a day.
So don't wait until your thirsty to drink a glass of water, you may already be dehydrated.