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Recommended Daily Water Intake


I know that drinking water is important.  How much should I be drinking each day?


Water is essential indeed!  If we don't ingest enough fluid, dehydration can set in quickly.  To gauge the importance of water relative to food, consider that severe dehydration can lead to death within a matter of days, whereas we can go for weeks without food.

Approximately 55-60% of our body weight is water.  That's why our body weight can fluctuate so dramatically and quickly… especially after exercise in the heat when we can lose large amounts of body water to sweat.  Our bodies depend on water to keep our cells and body systems running smoothly.  Most importantly, it is used to maintain blood volume, which is imperative for regulating body temperature and delivering oxygen and nutrients to the rest of the body.  Water also provides a medium for the biochemical reactions that occur at the cellular level.  In addition, water is crucial for the removal of waste products through the formation of urine by the kidneys.

It's important to realize that we can get our fluid requirements from the food we eat, as well as the fluids we drink.  For instance, an orange is 87% water!  Good sources of water are:

There are many different methods for calculating daily fluid requirements.  However, a simple equation to help adults figure their fluid needs is that for every pound of body weight, you need about half an ounce of fluid intake per day.  For instance, if you weigh 140 lbs., simply multiply 140 by .5 to estimate your daily fluid needs in ounces, then divide by eight to estimate your fluid needs in cups per day, rounding up to the nearest full cup.  [example:  140 x .5 = 70 ounces; 70 ounces divided by 8 = 9 cups of fluid per day]

0.5 ounces x Body Weight in Pounds = Daily Fluid Requirement in ounces

The other common way to calculate daily fluid needs is to base the fluid need on caloric intake.  1 milliliter of fluid for every calorie ingested.  Converted to the household measurement of ounces, your body needs .034 ounces for every calorie that you ingest.

0.034 ounces x Daily Caloric Intake = Daily Fluid Requirement in ounces

As you calculate out what your daily fluid requirements are, you'll probably realize that it is close to that common recommendation of 8 - 12 cups per day.  However, the above equations will give you a more accurate guideline because fluid needs vary depending on body size.  It's also important to realize that fluid requirements can vary dramatically under extreme conditions such as exercise, especially in hot and humid environments, and during illness associated with fever.  These situations require increased fluid needs.  Drink up!

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Our expert, Dr. Sharon E. Griffin, holds a B.S., M.S., and Ph.D. in the areas of exercise science/physiology.  She also holds a second M.S. degree in Nutrition and is a licensed nutritionist and an ACSM certified health and fitness instructor.
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