Water is the most needed chemical compound of our body. Without the daily necessary amount of water our body functions would be forced to shut down. The human body is anywhere from 55% to 78% water depending on body size. To function properly, the body requires between one and seven liters of water per day to avoid dehydration; the precise amount depends on the level of activity, temperature, humidity, and other factors. Most of this is ingested through foods or beverages other than drinking straight water. It is not clear how much water intake is needed by healthy people, though most advocates agree that 6–7 glasses of water (approximately 2 litres) daily is the minimum to maintain proper hydration. Medical literature favors a lower consumption, typically 1 liter of water for an average male, excluding extra requirements due to fluid loss from exercise or warm weather. For those who have healthy kidneys, it is rather difficult to drink too much water, but (especially in warm humid weather and while exercising) it is dangerous to drink too little. People can drink far more water than necessary while exercising, however, putting them at risk of water intoxication (hyperhydration), which can be fatal. The "fact" that a person should consume eight glasses of water per day cannot be traced back to a scientific source. There are other myths such as the effect of water on weight loss and constipation that have been dispelled.
Determine how much water you need. You've probably heard the "8 by 8" rule - drink eight 8-ounce glasses of water per day (2 quarts, 1.8 liters) - but the amount of water a person needs varies depending on his or her weight and activity level. Another way to determine your specific recommended water intake is to divide your weight (in pounds) by two. The resulting number is the number of ounces of water you need each day. For example, if you weigh 150 lbs., strive to drink 75 ounces of water daily. For those who use the Metric system, divide your weight (in kilograms) by 30 (ex. somebody weighing 70 kg is going to need 2.3 liters per day). Keep in mind that these recommended intake numbers are controversial and some experts believe they are a gross exaggeration. See "warnings" below for more information.
Signs of Dehydration. You lose water through urination, respiration, and by sweating. If you are very active, you lose more water than if you are sedentary. Diuretics such as caffeine pills and alcohol result in the need to drink more water because they trick your body into thinking you have more water than we need. Symptoms of mild dehydration include chronic pains in joints and muscles,lower back pain, headaches and constipation. A strong odor to your urine, along with a yellow or amber color indicates that you may not be getting enough water. Note that riboflavin, a B Vitamin, will make your urine bright yellow. Thirst is an obvious sign of dehydration and in fact, you need water long before you feel thirsty.
Dangers of Too Much Water. Don't start drinking an extra gallon of water a day - that can kill you, especially if you are fasting or eating very little. Water taken in must be in balance with body salt - electrolytes. The body needs to maintain salt balance or risk hyponatremia with heart attack and even death. Drinking too much water dilutes the salt in your blood and tissues - and can kill you. Healthy athletes have died from drinking too much plain water and not replacing salt. Dieters should not plunge into drinking gallons of water a day in hopes of burning a few more calories. Drink an extra few glasses, yes. But a gallon is too much.