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Water: How much should you drink every day?

Water is essential to good health, yet needs vary by individual. These guidelines can help ensure you drink enough fluids.

By Mayo Clinic staff

How much water should you drink each day? It's a simple question with no easy answers. Studies have produced varying recommendations over the years, but in truth, your water needs depend on many factors, including your health, how active you are and where you live.

Although no single formula fits everyone, knowing more about your body's need for fluids will help you estimate how much water to drink each day.

Health benefits of water

Water is your body's principal chemical component and makes up about 60 percent of your body weight. Every system in your body depends on water. For example, water flushes toxins out of vital organs, carries nutrients to your cells and provides a moist environment for ear, nose and throat tissues.

Lack of water can lead to dehydration, a condition that occurs when you don't have enough water in your body to carry out normal functions. Even mild dehydration can drain your energy and make you tired.

How much water do you need?

Every day you lose water through your breath, perspiration, urine and bowel movements. For your body to function properly, you must replenish its water supply by consuming beverages and foods that contain water.

So how much water does the average, healthy adult living in a temperate climate need? In general, doctors recommend 8 or 9 cups. Here are the most common ways of calculating that amount:

  • Replacement approach. The average urine output for adults is about 1.5 liters (6.3 cups) a day. You lose close to an additional liter (about 4 cups) of water a day through breathing, sweating and bowel movements. Food usually accounts for 20 percent of your total fluid intake, so if you consume 2 liters of water or other beverages a day (a little more than 8 cups) along with your normal diet, you will typically replace your lost fluids.
  • 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. Although the approach really isn't supported by scientific evidence, many people use this easy-to-remember rule as a guideline for how much water and other fluids to drink.
  • Dietary recommendations. The Institute of Medicine advises that men consume roughly 3 liters (about 13 cups) of total beverages a day and women consume 2.2 liters (about 9 cups) of total beverages a day.

Even apart from the above approaches, if you drink enough fluid so that you rarely feel thirsty and produce 1.5 liters (6.3 cups) or more of colorless or slightly yellow urine a day, your fluid intake is probably adequate. If you're concerned about your fluid intake, check with your doctor or a registered dietitian. He or she can help you determine the amount of water that's best for you.

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References
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  2. Valtzin H. "Drink at least eight glasses of water a day." Really? Is there scientific evidence for 8 x 8? American Journal of Physiology - Regulatory, Integrative and Comparative Physiology. 2002;283:R993.
  3. Rose BD, et al. Maintenance and replacement fluid therapy in adults. http://www.uptodate.com/home/index.html. Accessed March 2, 2010.
  4. Dietary reference intakes for water, potassium, sodium, chloride and sulfate. Institute of Medicine. http://www.nal.usda.gov/fnic/DRI//DRI_Water/73-185.pdf. Accessed March 2, 2010.
  5. Exercise and fluid replacement. Medicine & Science in Sports & Exercise. 2007;39:377.
  6. Campbell SM. Hydration needs throughout the lifespan. American Journal of Clinical Nutrition. 2007;26:5858.
  7. Nutrition and athletic performance: Position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine. Journal of the American Dietetic Association. 2009;109:509.
  8. Park S, et al. Pathophysiology and management of calcium stones. Urology Clinics of North America. 2007;34:323.
  9. Manz F. Hydration and disease. Journal of the American College of Nutritionists. 2007;26(suppl):535S.

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April 17, 2010

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