Water runs your body. Think about it; your body is 83% water, your muscles are 75% water, your brain is 74% water, and your bones are 22% water. You need water for every single metabolic process in the body. Water is necessary to digest and absorb nutrients and vitamins. It carries away metabolic waste and it helps 'flush' fat and toxins through the liver and kidneys. Water can improve energy, increase mental and physical performance, remove toxins and waste from your body, keep your skin healthy and glowing, and may even assist with weight loss. If you're dehydrated (and most people do fall short with hydration), your blood is thicker and your body has to work harder in circulation. As a result, your brain becomes less active, making it harder to concentrate and causing fatigue. Water is one of the fluids that lubricates and cushions your joints and muscles, protecting them from shock and damage. If the body is dehydrated, it may become much more susceptible to ailments. Drinking proper amounts of water can help reduce cramping of the muscles and fatigue. Water is critical for well-being and life. You can't live without any water for very long (8-10 days, less in many cases as compared to approximately 30 days for food).
In a research study that examined more than 20,000 relatively healthy adults for over 6 years found that high daily intakes of water (5 cups or more) were associated with significantly lower risk for fatal coronary heart disease events, even after adjusting for smoking, hypertension and body mass index. That's a powerful study and a powerful incentive to drink more water for great health!
A general health recommendation for WATER INTAKE is to divide your weight in half and drink that number in ounces. Keep in mind that hot weather, humidity, exercising, and sweating are all factors that would require you to up your water intake.
Source: 150 Healthiest Foods on Earth, written by Jonny Bowden, ph.D., C.N.S.