8 Glasses of Water per Day: Says Who?

From Gillian Mayman:

The idea that you need to drink at least 8 glasses of water a day is ubiquitous in American culture. I’ve had doctors tell me this. I’ve read it on credible medical web sites. I’ve listened to a professor of public health discuss this as if it is scientific fact.

However, there is no scientific basis for the “8 glasses of water a day” rule. Even more intriguingly, the origins are somewhat of a mystery….

Dr. Frederick J. Stare wrote a book in 1974 with Dr. Margaret McWilliams that contains one of the earliest known references in print to this admonition…..

However, what Dr. Stare actually wrote was:

How much water each day? This is usually well regulated by various physiological mechanisms, but for the average adult, somewhere around 6 to 8 glasses per 24 hours and this can be in the form of coffee, tea, milk, soft drinks, beer, etc. Fruits and vegetables are also good sources of water.“…

The origins of the “8 glasses of water a day” rule was explored by Dr. Heinz Valtin in a 2002 article and Dr. Tsindos  in a 2012 article. After extensive searches of the published literature, they found absolutely no scientific evidence for the idea that most people need to drink at least 8 glasses of water a day.

So how much water do we need? Clearly, athletes and people who live in very hot climates need more water. But for the average person, the amount of liquid that they take in just needs to match the amount that they lose through bodily excretions such as urine, feces, sweat, and exhaled water vapor. For women this is about 2.2 liters and for men it’s about 3 liters, according to the Mayo Clinic. [This translates to about 74 ounces for women and 101 ounces for men.]  However, the liquid that is consumed does not need to be water. It can be tea, coffee, soda, juice or other beverage. It can also come from foods that we eat which contain water.

About Scot McKnight

Scot McKnight is a recognized authority on the New Testament, early Christianity, and the historical Jesus. McKnight, author of more than fifty books, is the Professor of New Testament at Northern Seminary in Lombard, IL.

  • Tom

    I have always discounted that number. Throughout history how many societies do you think had access to eight glasses of water a day regularly? I think not.

  • LT

    Throughout history how many societies do you think had access to eight glasses of water a day regularly?

    Yes, and look at how many of those people are dead. :)

    I am just taking this opportunity to point out a bad argument. Whether past societies had access to 8 glasses of water a day is irrelevant to the point of whether or not we should drink 8 glasses.

    We may, in fact, not needed 8 glasses of water, but the water access of historical societies is an irrelevant argument.

  • Barb

    four coffees and four beers! check! just kidding!

  • http://www.twitter.com/aaronlage aaron

    First, and most relevant – 8 ounce glasses, 12 oz, 16 oz? which one? ‘glasses’ could be irrelevant unless you state the size.

    Also, I love how this article says “who came up with 8 glasses a day” like it’s an absurd thought and then finishes by saying men should really drink 3 liters – which is nearly a gallon!!

    Last of all, I’ve never thought of it as a ‘rule’ as stated in the article. It’s a cliche line based on what is optimal. Sure, you can survive on much less, but who wants to merely survive? I’d rather thrive.

  • http://shanescottonline.com Shane

    I would take issue with some aspects of this argument. First not all liquids are created equal. Drinks with caffeine have a diuretic effect so they can be counterproductive. And Scot since you are a big coffee drinker like me and you use your voice for a living like me it is important to keep the vocal folds hydrated.

    A better rule of thumb is oz of water per lbs weight of the person. Divide your weight and drink that many oz in hydrating fluids. In my case that’s Lake Michigan!

  • http://rising4air.wordpress.com MikeK

    Just a word to the wise here: All you have to get are kidney stones for the first time (or more than once…), and drinking water will seem like a common sense way to not only avoid unnecessary pain (and poor kidney health), but also to accumulate other health benefits. Those stones, though, have a unique way of persuading you of the value of high volume consumption of water.

    My initial response to the suggestion that the type of liquid consumed (see above list) is immaterial will likely be contested by urologists near and far…if you lick your lips right now, and they feel dry, you have my permission to get up and drink some water…and how much you ask? Enough to make you go…your kidneys will thank me later…

  • metanoia

    At my age, eight glasses a day only makes me get up 8 times every night. ;-)

  • Les Yoder

    I’m having some trouble understanding the last paragraph’s math. Normally we think of a glass of water as 8 ounces or 240ml. So for a man, if 101 onces is recommended -that is almost 13 glasses???

  • Johnny

    The “one type of fluid is as good as the other” bit is nonsense. An eight once glass of water contains eight ounces of water. An eight ounce glass of coffee contains and ounce or two of coffee and whatever else you put in it (cream, sugar, etc.) It’s physically impossible to have the remaining water equal 8 ounces. I’m with MikeK #6. We’ll see who has better kidneys in late middle age. My money’s on the person who drinks more water.


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