There's no easy answerto how much water you should drinkevery day.Just as you are unique, so are your water needs. How much water you need depends on many factors, including your health status, how active you are and where you live. Though no single formula fits all people, several guidelines are available to help you. Health benefits of water Water is crucial to your health. It makes up, on average, 60 percent of your body weight. Every system in your body depends on water.Lack of water can lead to dehydration, a condition that occurs when you don't have enough water in your body to carry on normal functions. Even mild dehydration can sap your energy and make you tired. Dehydration poses a particular health risk for the very young and the very old. Signs and symptoms of dehydration include:  Excessive thirst  Fatigue  Headache  Dry mouth  Little or no urination  Muscle weakness  Dizziness  Lightheadedness Every day you loose water—through sweating, exhaling, urinating and bowel movements. For your body to function properly, you need to replace this water by consuming beverages and foods that contain water. At least three approaches estimate total fluid (water) needs for healthy, sedentary adults living in a temperate climate: 1. Replacement approach. The average urine output for adults is 1.5 liters a day. You lose close to an additional liter of water a day through breathing, sweating and bowel movements. Food usually accounts for 20 percent of your fluid intake, so you if you consume 2 liters of water or other beverages a day (a little more than 8 cups), along with your normal diet, you can replace the lost fluids. 2. Eight 8-ounce glasses of water a day. Another approach to water intake is the "8 x 8 rule" — drink eight 8-ounce glasses of water a day (about 1.9 liters). The rule could also be stated, "drink eight 8-ounce glasses of fluid a day," as all fluids count toward the daily total. Though this approach isn't supported by scientific evidence, many people use this basic rule as a guideline for how much water to drink. 3. Dietary recommendations. The Institute of Medicine recommends that men consumeabout 13 cups of total beverages a day and women consume 2.2 liters (about 9 cups) of total beverages a day. These guidelines are based on national food surveys that assessed people's average fluid intakes. You can choose any of these fluid intake approaches to gauge how much water to drink. Your current total fluid intake is probably OK if you drink enough water to quench your thirst, produce a colorless or slightly yellow normal amount of urine, and feel well. Factors that influence water needs You may need to modify total fluid intake from these recommended amounts depending on several factors, including how active you are, the climate, your health status, and if you're pregnant or breast-feeding. 1. Illnesses or health conditions. Some signs and symptoms of illnesses, such as fever, vomiting and diarrhea, cause your body to lose extra fluids. To replace lost fluids, drink more water or oral rehydration solutions (Gatorade, Powerade, CeraLyte, others). When water loss can't be replaced orally, intravenous water and electrolytes may be necessary. Increased water intake is nearly always advised in people with urinary tract stones. On the other hand, you may need to limit the amount of water you drink if you have certain conditions that impair excretion of water — such as heart failure and some types of kidney, liver, adrenal and thyroid diseases. 2. Environment. You need to drink additional water in hot or humid weather to help lower your body temperature and to replace what you lose through sweating. 3. Exercise. If you exercise or engage in any activity that makes you sweat, you'll need to drink extra water to compensate for that fluid loss. Drink 2 cups of water two hours before a long endurance event, for example, a marathon or half-marathon. One to 2 cups of water is also adequate for shorter bouts of exercise. During the activity, replenish fluids at regular intervals, and continue drinking water or other fluids after you're finished.