We have all read (or been told) that drinking six to eight glasses of water each day is ideal for good health. But adequate water intake is dependent on a person's health status, activity level, and type of activity.
Some other factors environment, health status, and, for women, whether they are pregnant or breast-feeding. So a straightforward answer for the straightforward question "How much water should a person drink each day?" might go something like this: "It depends on the person."
What is clear is the importance of water to the human body: It is the body's primary chemical component and accounts for over half of a person's weight. Water is lost from the body on a daily basis by a combination of breath, urine and bowel movements, and, of course, perspiration. The body's natural way of replenish its water supply is consume drinks and foods that contain water.
Lack of water can lead to dehydration, a condition that occurs when the body has insufficient water to carry out normal functions. Even a mild case of dehydration can sap energy and cause fatigue. Unfortunately, the sense of thirst is often out of sync with the body's demands, meaning that if you experience thirst, you may already be slightly dehydrated. One proactive -- though not always practical -- way to avoid this state is to consume water before thirst occurs. To cover all the bases, a goal is to drink before, during and after exercise.
How Much is Enough?
The short answer and a common rule of thumb is that if someone drinks enough fluid so that he or she rarely feels thirsty and produce about 1.4 liters (a little over 6 cups) or more of colorless or slightly yellow urine a day, it is likely fluid intake is adequate.
The Institute of Medicine, an indepedent, non-profit ogranization whose stated mission is that it "serves as adviser to the nation to improve health" recommends that men drink a total of about 3 liters (roughly 13 cups) of beverages a day and that women drink 2.2 liters (roughly 9 cups) of beverages daily.
Although beverages are an obvious source, water is present also in many of the foods that we eat, such as fruits and vegetables. Food, in fact, accounts for some 20 percent of our fluid intake each day.
Activity Type and Intensity
How much additional fluid a person needs depends on both how much he or she sweats during exercise and the duration and nature of exercise. Each time a person works out, he or she needs to drink extra water to compensate for fluid loss. But how much? An extra 400 to 600 milliliters (about 1.5 to 2.5 cups) of water is recommended for short exercise intervals, but intense exercise sessions over an hour calls for more fluid intake.
And not all fluid is created equal.
Among marathon runners, for instance, a real concern is a condition known as hyponatremia. This causes the body's cells to bloat from too much water and not enough electrolytes. Some of its symptoms include confusion, nausea and convulsions. Not just for marathoners, the condition can also occur among the elderly and in hospitalized patients.
The solution is to consume a solution of water and electrolytes commonly found in many types of sports drinks to reestablish the body's equilibrium.
Hot and/or humid weather even without exercising or engaging in activity is enough to cause perspiration and requires additional intake of fluid. Heated indoor air also can cause your skin to lose moisture during the cooler months. In addition, altitudes over 8,200 feet (2,500 meters) can lead to an increase in urination and more rapid breathing, which in turn depletes any fluid reserves.
Fever, vomiting or diarrhea all cause the body to lose fluids. But in some instances, conditions such as heart failure and several types of kidney, liver and adrenal diseases can slow water excretion and call for a limit on fluid intake.
The Institute of Medicine suggests that pregnant women drink 2.3 liters (approximately 10 cups) of fluids each day, while women who are nursing should consume 3.1 liters (roughly 13 cups) of fluids daily.
These recommendations are all for an apparently healthy individual. Excessive thirst and increased urination could be indicators of a more serious medical condition. Consult your physician if either of these conditions are present.