Just How Much Water Does the Body Need?

How much liquid should we be consuming in a day? Individual needs vary, but in 2005 the Food and Nutrition Board of the Institute of Medicine (IOM) established dietary reference intakes for water.

The daily quantities recommended by the IOM were stated in terms of total water--that's the technical name for the total amount of water contained in all the foods and beverages you take in during a day. (Even caffeinated drinks count.) Here's what the IOM says people ages 19 to 30 years must drink to maintain normal hydration:

• To be adequately hydrated, a woman should consume an average of 91 ounces, or 11 (8-oz) cups of total water every day.
• To be adequately hydrated, a man should consume about 125 ounces, or 15.6 (8-oz) cups of total water every day.

How much of this inner irrigation must I actually swallow in liquid form?

The IOM states that 80 percent of our total water comes from the fluids we drink, and that we get the other 20 percent from the foods we eat. If you multiply 11 cups of fluid (the total amount that a woman needs to take in) by 0.8 (to find out what 80 percent of 11 is), then you get 8.8 cups--so a woman must actually drink about 9 cups of liquid every day (with the remaining 20 percent supplied by the foods she eats). Using the same arithmetic, a man must drink a little less than 13 cups of fluid a day.

That's a lot of fluids. And the panel says that those who are very physically active or who live in a hot climate might need to consume more. But don't try to work up to your required number of cups in just a day or two; give yourself some time to meet your quota.