Every day, you lose water through breathing, urination, sweating, and bowel movements. It is important to replace lost water by drinking beverages and eating foods that contain water. How much water you need to replace daily depends upon your body configuration, lifestyle, metabolism, general health, and the physical environment in which you live.

For healthy adults in temperate climates, there are two common approaches to determining how much water to drink each day.

The replacement approach starts with estimates of daily water losses, about 2.5 liters per day. Roughly 20 percent of that is replaced by eating a normal diet. So, generally, you need to drink about 2 liters of water-rich beverages per day, or eight cups' worth of water.

The dietary approach is based on guidelines issued by the Institute of Medicine. Adult men should consume 3.0 liters (13 cups) of beverages per day, while women need 2.2 liters (9 cups).

A rule of thumb is to drink enough, often enough, so that you do not feel thirsty during the day. If you produce one to two liters of colorless of slightly yellow urine per day, you are probably getting enough water.

The more you exercise, the more water you lose through sweating. An extra 1 to 2 cups of water suffices for a short workout. During strenuous exercise lasting more than an hour, consume 13 to 26 ounces (2 to 3 cups) of water per hour. Increase water consumption in hot weather exercise.

For long periods of exercise, sports drinks containing sodium should be consumed instead of plain water. Sodium is lost with sweat, and this metal is essential in maintaining the body’s electrolyte balance.

Altitudes greater than 2,500 meters (8,200 feet) can trigger increased urination and more rapid breathing leading to a greater rate of water loss. Drink more at higher elevations.

Illness is often accompanied by increased sweating, vomiting, and diarrhea, all water losses that need replenishment. Drink plenty of fluids when ill, including fruit juices, sports drinks, and that good old panacea, chicken soup!

Pregnant and breast-feeding women have greater water needs, too. The Institute of Medicine recommends that pregnant women consume 2.4 liters of beverages per day, 3.0 liters for breast-feeding women.

Water need not come from a tap or bottle to satisfy the Institute's guidelines. Many fruits and vegetables are nearly 100 percent water by weight. Milk and juice are mostly water. Even beer and wine, decaffeinated beverages such as coffee, tea, and soda can be healthy water substitutes.

Mild dehydration can result from losing as little as 1 to 2 percent of one's normal water weight. Symptoms of dehydration include mild to excessive thirst; fatigue; headache; dry mouth; little or no urination; muscle weakness; dizziness; and lightheadedness. While mild dehydration is quickly cured by drinking water, severe dehydration can be life-threatening and require delivery of fluids intravenously.

Too much water can be as dangerous as too little. "Water poisoning" upsets the balance of chemicals in the body and can kill. Symptoms of water poisoning include disorientation; hallucinations; and unconsciousness. Immediate medical treatment is vital.

Drink enough beverages each day to avoid thirst and dark, strong-smelling urine, and you can be pretty sure you are getting enough water. How much water to drink is a hot topic in developed countries. Stay healthy and drink enough.