National Geographic News
High school football players drink water in Brainerd, Minnesota.

Brainerd High School football players drink water to stay hydrated during practice in hot weather.

Photograph by Steve Kohls, Brainerd Dispatch/AP

Marc Silver

National Geographic

Published September 13, 2013

"I've come to realize that if we were going to take just one step to make ourselves and our families healthier, probably the single best thing we could do is to simply drink more water," First Lady Michelle Obama said in a statement issued this week. She went on to recommend downing an additional glass a day.

Which raises the question: How many glasses of water a day should you drink?

It's commonly believed that eight 8-ounce glasses of water should be guzzled each day. You sure won't get any arguments about that from the bottled water industry. But hydration experts aren't sure where the "8 x 8" rule came from—or whether it holds water.

Mike Sawka, a U.S. Army research scientist, thinks the origins lie in a 1933 study on rodent hydration. The research led to a recommendation of 2.5 liters a day, or 84.5 ounces of liquid, for a moderately active human to make up for water lost to sweat and excretions. He says that 20 percent of those ounces come from foods that contain a lot of water: soup, ice cream, celery. That leaves 67.6 ounces of water, or roughly "8 x 8."

Only you don't really need eight daily glasses. Other beverages count, even if they're caffeinated. "The body's need to keep fluid trumps the small influence caffeine might have on losing fluid," says University of Connecticut exercise physiologist Douglas Casa.

Besides, it's not like you need to line up eight glasses and down 'em or risk dehydration. The basic rule: Drink if you feel thirsty. If not, don't. The exception would be folks about to embark on an intense workout. Drinking beforehand is helpful.

And if you're worried that you're not drinking enough, check your urine. Dark yellow, says University of Pennsylvania nutritionist Stella Volpe, is the color of dehydration.

23 comments
Mike Tyburski
Mike Tyburski

I drink about 2 to 3 liters daily and tell people. It's fine to drink too much pop or coffee at times. But, they are not drinking enough water! or any...

Macy Desmarais
Macy Desmarais

I have heard that you are supposed to drink around half of your body weight in ounces of water per day. 

Linda Lesher
Linda Lesher

I drank 10-12 glasses of water daily and like Phil I was flushing out my electrolytes.  Now I drink about 6 glasses a day and I'm fine.

Phil R
Phil R

I used to drink 10 glasses of water a day (10-12 oz apiece) religiously. I found out later that I was flushing out all of my electrolytes. I've scaled down to about half that, and I actually feel physically better. As the article states, as long as the urine is clear, all is well.

Lynne L.
Lynne L.

The point our First Lady is making to kids is to drink more water and less sugary liquids. This IS new news to some people who never reach for water to satisfy thirst. Add some fresh lemon and give yourself more good to drink!

Thys Du Plessis
Thys Du Plessis

Should mind for 'water poisoning'....Liquid can be taken in by means of other beverages, not necessarily water.

Valeria M.
Valeria M.

I should start drinking water more often!! I'm getting a glass right now

Teri W.
Teri W.

Different people need different amounts. I was told by my doctor, who specializes in nephrology (kidney), that I needed to drink at least 3 liters a day because I have had numerous episodes of kidney stones. This amount works for me and I feel better when I drink that amount. My mother had been drinking 3-4 liters a day and was having kidney pains that her doctor told her were spasms because she was drinking too much and not allowing her kidneys to rest. We are about the same height/weight.

William Thiel
William Thiel

We are all different, size, age, weight and what we do during the day as work, play and exercise. Some days, depending on heat, work and erercise, I'll drink several quarts of liquid, water, tea, beer and if I'm not busy somedays, I'll drink only a cup of coffee, a glass of juice and perhaps a coke. I may go two or three days and never drink any WATER. When I do that my lips become very dry and I have drymouth at night.

anna krygier
anna krygier

I come from a country where not many people drink water. An average person ingests about a glass of tea, a cup of coffee and occasionally a glass of juice or soda - per day. Nobody looks, feels or functions differently because of that.

John H.
John H.

What is funny is that diet soda (diet coke) is 99% water. A fact few people know. I am not saying the 1% is good for you but it is still in my opinion a unknown fact.

Courtney McGregor
Courtney McGregor

I've heard the 8 x 8 pronouncement before and many strong opinions about the importance of it. But where is the data? And I don't mean anecdotal experience. Have studies been done with proper controls?

Janine Starykowicz
Janine Starykowicz

"Drink more water" means instead of soda and other highly sweetened drinks. Most people do get enough liquids, but they are getting high calorie junk food liquids. Buy a decent water bottle, get a filter if you don't like the taste of your tap water. You will save money, lose weight, and feel much better.

DONALD PRINCES
DONALD PRINCES

I AM LOOKING FOR MY DAUGHTER OPHELIA WHO LIVED AT 7715 SO EMERAL SOUTHSIDE OF CHICAGO.IL D.O.B.AUGUST 18TH 1968 MARRIED HAS A SON AND DAUGHTER MOTHER NAME IS MAYBELL, DADDY WILL NEVER STOP LOOKING FOR YOU ARE YOUR BROTHER JUWAN Mc CLOUD MOTHER NAME IS RUBY

Bolívar Lituma Ortega
Bolívar Lituma Ortega

If aperson drinks 8 glasses of water every day, probablyhe/she isn´t going to eat, lunch or dinner ¨cause his/her bellies are full. Can you explain me that, please. thank you.

Karen Panasewicz
Karen Panasewicz

i totally disagree... you ought to drink half  your weight in ounces.... your brain needs it the most... 

HELLO? I'm a CMT and see the effects of people who do not drink enough water firsthand... 

and NO.. other beverages do not count... seriously... no... they DO NOT count..


Roiikka-Ta P Globetrotter
Roiikka-Ta P Globetrotter

ive noticed that the more foods that are "bad for you" the less water you drink. i think she is stating a simple fact. the more water you drink, the more healthy you are. too much of anything though isnt really good for you ..

Dan Libby
Dan Libby

It's good to plan ahead and drink before and during activities that dehydrate. Don't wait until you're already thirsty and dehydrated, you may be affected before you know it. I found motorcycle riding to be very dehydrating, especially racing. Carry lots of water and drinking every rest stop keeps you hydrated and you function better, safer. 

John C.
John C.

Your body knows when it needs water, you get thirsty.

jake ki
jake ki

@Karen Panasewicz 

I'm a medical doctor - and sorry, other beverages do count. The half your weight in in ounces myth is lacking any scientific data at all. In fact, in my ER, we regularly see patients who have overhydrated - a condition called hyponatremia, an electrolyte imbalance. People lacking a scientific background like yourself contribute to the myths that lead to over hydration. So please, let the folks qualified to dispense such advice guide your judgment in areas like this. A CMT is not such a person. 

Emily D.
Emily D.

@John C. I would usually agree, except when you are focused on other matters, dehydration can set in  and surreptitiously take its toll.

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