The mysterious origins of the “8 glasses of water a day” rule

by Gillian Mayman on October 22, 2012

An illustrated guide to parenting with science.

My ten year old is a world champion picky eater. His diet is basically limited to frozen waffles, pizza, and cereal with milk.

This made it especially panic-inducing concerning when he came home from school last week complaining that he had to drink water. Did he not like water anymore?

It turns out that his teacher had admonished the class to drink at least 8 glasses of water a day. He was even required to keep a “water journal” to track how much water he drank every day for a week.

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.

It might be this man’s fault.

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.

How much water each day? .. for the average adult, somewhere around 6 to 8 glasses per 24 hours

This is how most of us understand the issue.

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.

You can see that Dr. Stare understood the two most important points that are generally lost when people discuss how much water is needed every day.

  1. This is usually well regulated by our bodies. This is not something the average, sedentary person needs to be overly concerned about. We eat, we drink, and it takes care of itself.
  2. This can be in the form of other liquids and food. It does not need to be actual water. It can come from pasta or yogurt or an apple.

So why do we all think that we need 8 glasses of actual water each day? Dr. Stare seems to blame the rumor on this man.

Dr. Irwin Stillman created the popular “Stillman Diet” in 1967 and it is a precursor to the more modern Atkins diet. Dr. Stillman very clearly specified that eight glasses of water were needed each day and even offered a specious biological argument.

Dr. Stare is clearly dismissive of Dr. Stillman’s advice when he discusses the Stillman Diet:

[Dr. Stillman] insisted on a minimum eight 10-ounce glasses of water daily… The reason for the eight glasses of water is to provide sufficient water for the kidneys to use in washing away the fatty acids resulting from the breakdown of fat, says Dr. Stillman. A bit later, however, he writes, “The ‘why’ of this functioning is not fully understood.”

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.

There is an argument, of course, that water is a much better source of liquid than coffee, soda, or juice. There is certainly a case to be made regarding calories, sugar, and caffeine. But in terms of liquid intake that is needed, the average person’s body does not really care about the form that liquid takes.

Erik Cox October 22, 2012 at 8:43 am

Excellent – always wondered where we got that notion from. I’ll stick to coffee.

Brash Equilibrium October 22, 2012 at 9:41 am

The Google Ngram linked below appears to confirm the Stillman effect (although it may be confounded by the Stare effect). There are, however, curious blips before either of them were popular (or in some cases even born).

Gillian Mayman October 22, 2012 at 9:45 am

I LOVE this! Thank you for sharing. Honestly, I’m hoping that someone leaves a comment with better evidence for where this rule comes from. As I mentioned in my post, the two recent published reviews of the topic did not turn up much. Stare and Stillman were the two biggest leads that they found.

Angela October 22, 2012 at 9:45 am

Thanks for this post! Eight glasses of water for a child – oh dear! If my dad could read English, I would actually send this to him, before he keeps on forcing further family members on this regimen that I instinctively dismissed. 😉 I take it that there is a similar myth surrounding the extent of dehydration from caffeine or alcohol?

layogenic November 5, 2012 at 4:25 pm

Caffeine has a diuretic affect after about 500mg a day (5-7 cups of coffee), so, yes and no. Alcohol is more powerful because it blocks ADH (a hormone that triggers water re-absorbtion, esp. in the kidneys pre-urine production), which can lead to a lot of trips to the restroom and loss of water vs. uptake, depending on what you’re drinking.

Drjuliebug October 22, 2012 at 11:17 am

Unquestioning acceptance of the 8-glass rule came close to killing my mother several years ago. At age 89, she was having some of the fluid vs. electrolyte balance problems that become common when your heart and kidneys are that age. She began to feel vaguely unwell, remembered her doctor’s advice about staying hydrated, and made sure to down those 8 glasses even though it made her feel worse. After a month or so of this, she wound up in the ER with hyponatremia, and then in a nursing home for two months of rehabilitation from the ensuing weakness, malaise, and mental confusion. Fortunately, she recovered — she’s now an amazingly active 93, and she and her (new!) physician monitor her fluid intake very closely.

John October 22, 2012 at 11:57 am

Dear dear dear….
Did anybody care to do the conversion? So, just how many 10oz glasses of water are there in 2.2 to 3 litres?

This kind of dumb should not be in print. Certainly not purporting to be debunking anything.

Squirrel Nutkin October 22, 2012 at 12:39 pm

Is 2.2-3 litres about seven-and-a-half to ten 10oz glasses?

So is the Mayo clinic estimate of the daily water of similar scale to that of Dr Stare in 1974?

So they have a similar estimate of the amount of water ingested by all routes which thanks to the healthy body’s mechanisms matches the amount of water excreted/sweated/exhaled/etc?

So that doesn’t effect the article’s clear explanation that making yourself actually drink about 8 glasses of water is a misunderstanding of the real physiological process?

So the point of your comment was…?

Gillian Mayman October 22, 2012 at 12:59 pm

The 2.2 – 3 liters refers to the amount of liquid that your body needs in a day not the amount of water that you need to drink. The argument is against needing to drink 8 glasses of actual water a day not against the fact that your body needs to take in a reasonable amount of fluids.

G. Armou Van Horn October 22, 2012 at 1:31 pm

Another teaching moment, but one that *really* shouldn’t be needed. John, you’re sadly living in a place that still uses ounces (and degrees Fahrenheit) in conversation, but that doesn’t mean you have any excuse for not knowing the real units. First, there are 80 ounces of water in eight 10-ounce glasses, so you could just type “80 ounces to liters” in any browser’s address or search bar and come up with 2.36588 in a fraction of a second.

But really, eight 10-ounce glasses is the same as ten 8-ounce glasses. Two times eight ounces is a pint, so that’s five pints, and even if your only exposure to units of measure come from buying pop at the grocery store you know that two pints is a quart and a quart is roughly a liter and you know what a 2-liter bottle of pop looks like.

So what you can see if you have any grasp of units of volume is that someone was recommending that people drink their entire water content as plain water, in addition to the water they were already taking in.


sparkles October 28, 2012 at 11:13 am

I think John has some kind of a point (although not a very polite one). The paragraph begins with “So how much water do we need?”, which sounds pretty similar to “So how much water do we need to drink?”.
The question makes it sound like we’re about to turn the 8 glasses idea on its head, when in fact, the number comes out about the same. So it turns out, we do need to put in about 8 glasses of water a day, it’s just that it doesn’t matter what package that water comes in.

Margaret October 22, 2012 at 2:18 pm

Good article, I have a student right now that is very active she drinks more than the recommended amount of water and says she does this on doctors advice. They carefully calculated how much water she would use a day. I learned from this that everyone is different, but on average we should still get between 2 and 3 liters of liquid a day.

As a math teacher I don’t like switching between types of units in a post. If you are going to use ounces… then 10 ounces is approximately .3 liters making 80 ounces about 2.4 liters a little less than that but approximately. Most people don’t know how conversions work in either direction. They know what they learned growing up, but that is it.


Gillian Mayman October 23, 2012 at 8:13 am

Thanks, Margaret. I completely missed the fact that I switched types of unit in the post. I made the correction just now.

Micayla October 22, 2012 at 4:49 pm

‘For women this is about 2.2 liters and for men it’s about 3 liters,’

In other words, it is not a myth at all. It is accurate information. 2.2 -3 liters = 74.4 – 101.4 ounces. Additionally, coffee and other caffeinated beverages do *not* count toward this amount, as caffeine is a diuretic.

Gillian Mayman October 23, 2012 at 8:25 am

A review of the literature found that “Doses of caffeine equivalent to the amount normally found in standard servings of tea, coffee and carbonated soft drinks appear to have no diuretic action.” The full article is here: (I think it’s freely available. My apologies if it’s not!)

renem October 22, 2012 at 11:09 pm

sorry micayla that isn’t true at least for the majority of people

Steph October 23, 2012 at 2:26 am

Interestingly, here in France the recommend amount is 1.5 liter (about 50 ounces?). It would be interesting to trace back to where the difference emerged.
Also whatever happened to simply looking at the coloration of your urine. If it’s too concentrated then drink more!

Anne Masters October 23, 2012 at 12:08 pm

This could not be more wrong and is TOTALLY irresponsible. These “scientists” (and I’d like to see what affiliations they have with soda or coffee manufacturers) don’t do their own research, they just look through an undisclosed and absolutely incomplete number of published works and tell us that we get water from the world’s least healthy foods?

Coffee is not only a diuretic, meaning it dehydrates, not hydrates, but it is completely acidic, which leads to things like…CANCER. Same goes for soda and other crap mentioned here. Oh, and you forgot diabetes.

Maybe western doctors (who get 2-5% of their education on nutrition, which is why western medicine is the third leading cause of death in North America) and scientists shouldn’t make up for the extent of your “reporting.” A good doctor will tell you that basic science no one needs a degree to understand is that our bodies are full of toxins, largely from what we eat, and we need to flush our bodies, which are made up primarily of water, of these toxins with the purest available remedy – WATER. Not coffee, not soda.

And I think we should all beware of any blog/article that starts off with a parent admitting their child eats mostly pizza and frozen waffles. It’s mighty telling.

I can’t believe you published this as fact.

Andrew Maynard October 23, 2012 at 1:59 pm

Dear Anne,

I assume you read the commenting guidelines for this site ( While I do encourage strong comments, I also expect commenters to respect the writers, remain civil and constructive, and understand the context of the blog. And not launch ad hominem attacks on my students!

Thank you

Andrew Maynard

Matt Shipman October 23, 2012 at 2:12 pm

Hi Anne,
the author here clearly noted the advantages of water over soda, juice or coffee (see the last paragraph). However, if addressing solely the issue of liquid intake, those beverages (however one feels about them) seem to do the trick.

Also, while coffee contains caffeine (which is a mild diuretic), research has found that it does not contribute to dehydration. The Mayo Clinic (which is widely respected) addresses that very question here: Note that they do not recommend drinking caffeinate beverages, they simply note that they’re not dehydrating (which is the same point made by the author of this blog post).

On a final point, as a parent, there are days when it’s might tough to convince a kid to eat the healthy food. I’ve certainly had “pizza nights” with my children. And, based on how my kids are turning out, I don’t think I’m a failure as a parent. Of course, based on your remarks above, you might disagree.

Shara E October 23, 2012 at 2:16 pm

Anne, respectfully as possible, could you please give some background information/support for “western medicine is the third leading cause of death in North America”?

Second: To quote an earlier comment from Gillian: “The argument is against needing to drink 8 glasses of actual water a day not against the fact that your body needs to take in a reasonable amount of fluids.” , moreover she also addresses at the end that this piece is *only* about looking at the 8-glasses rule, not taking into account other factors such as diuretics etc. Also, to quote Gillian again:

A review of the literature found that “Doses of caffeine equivalent to the amount normally found in standard servings of tea, coffee and carbonated soft drinks appear to have no diuretic action.” The full article is here: (I think it’s freely available. My apologies if it’s not!)

Third: You make *several* very sweeping comments, with little to no backup for them (see the first point, also: where the data that Gillian was using came from, etc). Additionally, she never suggested you don’t need liquids to flush the body, and maintain fluid balance. Respectfully, you seem to have viewed this article *only* through the lens of your clear desire to go on a tirade about your own negative perceptions of Western Medicine and scientific research. Yes, a good doctor will tell you that you should be drinking water for many reasons, not just because of an 8×8 water rule, but they also do not immediately jump on the COFFEE = CANCER bandwagon. Excessive intake of pretty much anything, and yes this includes water, can be bad for you.

Additionally, while you may disagree with what Gillian wrote, there is no reason to respond with vitriol, particularly by attacking her or her parenting skills. Please keep in mind that part of the goal of these blogs is that they be entertaining and interesting, and that hyperbole is a beautiful thing! You seem to be taking everything she wrote as absolute, utter fact. It’s mighty telling.

We love to receive feedback on our blogs, but this was less-so feedback and more-so you choosing to use this post as a platform for your own agenda. Please do give us more feedback in the future, but not if it’s going to involve completely unwarranted personal attacks on the writers or obvious platforming for your own personal agenda. As you may have gathered, we feel very strongly about defending our own!

Thank you,

Gaythia Weis October 23, 2012 at 2:25 pm

As someone who had interactions with public schools in ways that intersected being a parent and a scientist, I am curious as to how you handled the “water journal” issue with both the student and the teacher. Did the final graphic here get shared with the class? I bet they would have loved it. But science/child raising/public school communication issues are perhaps material for another post.

Camryne October 23, 2012 at 8:05 pm

Since nobody else has brought it up, I will; Children are not adults, and to insist that they ingest water (or anything) in amounts based on research done on adult bodies is a bad idea. I would feel more comfortable making sure the children know that that is current accepted advice for the adult human body, not a child’s. There was no mention of it, but I think that no part of the child’s grade should be based on whether or not he ingests the suggested quantity, rather that the focus should be on observation, recording and perhaps summarizing what he’s observed. Making children aware of what they ingest is a great idea, and can be a great learning tool, especially when they learn through comparison of their data that although most have similar outcomes, there are variances to be expected, and that is tolerable and normal. Instead, I think that all of these children will probably “tweak” their journals to reflect what they think is expected of them. It could have been presented differently.

Matt Stone October 23, 2012 at 10:54 pm

Here’s a beauty on water dogma for ya…
Drinking too much water is actually quite a health liability, and one of the most frequent mistakes I see health-conscious people make.

Angela October 25, 2012 at 9:46 pm

There is a spoof in the Onion today on this, actually, entitled ‘Cactus Scientists Recommend Drinking 8 Cups Of Water Per Year’:,30094/

Matt Stone October 23, 2012 at 11:00 pm

Oh and Anne,

There is not a single drop of water in our bodies, if you define water as something similar to what comes out of a faucet or bottle of Fiji. It’s full of tons of salt, calcium, magnesium, and other things. It’s more like seawater than it is Aquafina. You certainly won’t see any doctor pumping water into someone’s veins. Not that water is all bad, but it’s certainly overrated, and not something anyone would choose when other options are available.

Anne Barna October 25, 2012 at 11:36 am

I think this concept is particularly sticky because we tend to think of water as “pure” and we can’t see the water that’s within food.

evilDoug October 25, 2012 at 5:56 pm

I recommend Respectful Insolence to anyone with further interest in the nonsense of “toxins” and the supposed evils of acids from diet, the fraud of the alkaline water machines, und so weiter.
Here’s a starting point:

Nathan Myers November 1, 2012 at 3:01 am

When a co-worker made fun of me for how much water he sees me drinking, my response was, “You talk *just like* someone who’s never had a kidney stone.” I strongly recommend, for all of you who, like him, have never had a kidney stone, against the experience.

Really, once is more than enough.

Doug November 2, 2012 at 11:39 am

I found Gillians information informative and entertaining. I now have a better understanding of the why’s and wherefor’s of the “8 glasses of water per day” rule. I usually drink water as my main form liquid – with coffee and tea in there as well – but I always had difficulty getting to the 8 glasses per day. Now I won’t be concerned. Thank you.

Lisa November 5, 2012 at 3:33 pm

Geez, just drink so that you’re no thirsty anymore. Problem solved. This nit picking is ridiculous!

Michael February 25, 2013 at 4:58 am

John Harvey Kellogg, yes the guy who along with his brother created Kelloggs Corn Flakes, is actually the one who came up with the idea of 8 glasses of water a day. He is responsible for coming up with this and many other “health” tips while working as chief medical officer at the Battle Creek Sanitarium in the late 1800’s. None of it was ever proven scientifically. The guy also condoned circumcision on boys and applying carbolic acid on a womans clitoris to prevent masturbation and sexual arousal.

Michael February 25, 2013 at 5:05 am

Oh and to answer your question as to how many glasses of water you need to drink, nature gave us the ability of thirst to come up with the answer for ourselves. Drink enough so that you’re not thirsty. Funny how mother nature has a way of figuring out all this hard scientificky stuff for us, huh?

Al March 15, 2013 at 6:09 am

Water intake is pretty easy to monitor, just look at your pee! It should be darker in the morning and then get light in color during the day.

Ali May 5, 2013 at 4:14 pm

Oh Heaven forbid this evil teacher push addictive and harmful water on your child. How dare she spread the socially damaging stigma of drinking *water*. Ugh, I hope you protected your kid and set him up for success by giving him buckets of soda and high fructose juice to wash down his box waffles, cereal, and well balanced pizza.


Shay May 13, 2013 at 6:49 pm

Ali, can you just re-read what you wrote and then tell me that it wasn’t completely unnecessary?

Clearly, you simply read the first few sentences and based your comment off that. But, as another comment stated, children are not adults. And, as studies have shown and as facts will tell you, drinking too much water can be bad for you. Adults “having” to drink 8 glasses of water a day is less-than-factual (as your body DOES need between 2-3 ounces of water, which can be found in other liquids as well). For KIDS “having” drinking 8 glasses per day, when most of the comments above will tell you that it isn’t particularly necessary for adults? That can be potentially harmful, as drinking too much water can actually cause water intoxication and an imbalance in the water-electrolytes scale. Like I said, the average person needs between 2-3 liters of LIQUIDS, including coffee, tea, juice, etc. However one feels about the drink, I’m talking strictly the water one intakes while drinking a cup of coffee or a juice box or a can of soda.

Also, the author of this article never once complained about having to give her son water. What sensible parent would complain about giving their child water? Perhaps the teacher should have done a bit of research before giving her students this ridiculous assignment. If I were a mother of a student with such a teacher, I’d have a problem, as well.


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