Glug glug glug … why those eight glasses a day don’t HAVE to be water (or eight).

The super successful campaign to persuade people to drink vast amounts of bottled water really has two parts.

One part, which we have already talked about, is to persuade people that tap water is dirty and harmful, while bottled water is clean, pure and healthy – not to mention aspirational.

The other part is to persuade people that they have to glug down vast quantities of water – not just liquid, water specifically – every day to stay healthy.

This latter part, it turns out, is just as much of a crock as the first bit.

It is A MYTH. An Urban Legend, peddled in the media and on the internet, and repeated by word of mouth, so often that many people believe it is true.

The standard version of it, repeated ad nauseam, is “drink eight glasses of water a day”. So prevalent is this message that even rather good newspaper articles like this one, which squarely nail the giant bottled water sales-fest, trot it out without question.

Sometimes you are also told how big the glasses should be: “eight ounces”, which to us metric European types is just under 240 milliliters (ml).

Thus the advice is sometimes short-handed (especially in the US) as “8 x 8” or “8 by 8”.

BUT… it turns out there is a big, big, piece of bullshit floating in this glass of nostrum.

Wait for it…

Any fluid will do!

Yes, as trailed in the title, the fluid doesn’t need to be water.

Truly. The total amount of “fluid intake” being suggested here (1900 ml per day, so nearly 2 litres) is sort-of reasonable (though still anywhere from 10 to 50% above what scientists and doctors think of as the normal daily drinking requirement), but it can be ANY fluid. Everything that you drink counts.

Water. Coffee. Tea. Herbal tea. Beer (yes, beer). Wine (yes, wine).

But…. If you knew that, then you wouldn’t need to keep slurping down water. Not to mention buying it in handy bottles.

So why DO so many people carry on with the endless water-sipping?

Answer: Because they have bought the message.

But… why weren’t we told 8×8 wasn’t true? And where does 8×8 come from?

Here is where it gets interesting. No-one seems to know. The evidence that the “8 x 8” figure was totally unscientific has been around for ages. And to most scientists, the idea that “only clear water counts as fluid” is so transcendentally silly that they probably never thought anyone would be crazy enough to believe it.

But people clearly did. So perhaps some eminent scientist needs to review the scientific literature, and explain just exactly why all the legends peddled by what I call the “Hydrationistas” are nonsense?

Well, it has been done. You can find a comprehensive scholarly demolition of all the water myths peddled by the Hydrationistas in a review written by Professor Heinz Valtin for the American Journal of Physiology here.

Heinz what…?

Heinz Valtin is an Emeritus Professor of Medicine and Physiology, noted for his seminal research over 40 years on how fluid output from the kidney is controlled. He originally qualified as an MD (medical doctor) and is the author of three textbooks on kidney physiology. Valtin was Head of a well-regarded Physiology department in the US (at Dartmouth University) and trained many other notable kidney physiologists and nephrologists (kidney doctors) over the years.


Above: Heinz Valtin and furry friend

Valtin is probably best known in science for his work on the Battleboro rat. This is a rat strain which does not produce any vasopressin (anti-diuretic hormone) and thus cannot concentrate urine (vasopressin is the hormone, released in the brain when your body is a bit short of fluid, that signals to your kidney to reabsorb water extra-efficiently).

Brattleboro rats, lacking the signal hormone, cannot reabsorb water very efficiently and thus cannot produce concentrated (v. dark) urine. So they pee out lots (and lots) of dilute wee. They compensate for this by drinking bucket-loads – it can be the equivalent of 70% of their body wt a day – and the famous picture above shows a Brattleboro rat with a beaker containing its daily fluid intake. Brattleboro rats, which are a natural “vasopressin knockout animal”, in the jargon, have lots of uses in research. However, what they show us very clearly – just by looking at the picture – is that your kidney urine output, and water intake, adjust to match one another.

This is a slight over-simplification, since you take in water other ways than drinking (in what you eat, about 1000 ml /day), make some water via cellular respiration (about 300 ml / day) and lose water other ways than via the kidneys (in poo, about 100 ml / day, and via sweating and via evaporation from your mucous membranes and lungs, around 800 ml / day). But the basic principle is good – if you drink more, you will pee more. There are people with the same kind of problem as the Brattleboro rat (lack of urinary concentrating ability). They have a rare disease called (slightly confusingly) ”Diabetes_insipidus”, or more specifically “Central Diabetes Insipidus” if their problem arises from lack of vasopressin secretion from the (central) nervous system.

Er… what was all that stuff for?

The purpose of this lengthy preamble is twofold: first, to acquaint you with some basic principles of fluid balance and fluid and electrolyte physiology (including that good old rule: In = Out); and second, to make clear why what Heinz Valtin doesn’t know about body fluid balance isn’t worth knowing.

So what happened when Valtin went looking for the source of the “eight glasses of water a day” line, and for any evidence that it was based on any science, or that drinking this much was beneficial?

The answer is simple.

He couldn’t find any evidence. Not one bit.

The source of the 8×8 advice is a real mystery. The best guess Valtin has was that about 60 years ago, round about the end of WWII, a US Govt report said something like “the total amount of all fluids you need to drink a day is about the equivalent of eight glasses of water” – although this was not based on any particular scientific study.

Over time, and with the aid of the Water-Nuts and of literally billions of pounds/dollars in marketing spend, this has been transformed into “Eight glasses of water – you must drink this! – and other liquids don’t count!”

The other “Hydrationista Myths”

In his review Valtin also nails many of the other silly, but widely repeated, lines the Hydrationistas employ:

“Caffeinated drinks don’t count as part of your fluid intake, because they dehydrate you”

Not true. Of course they count – they are mostly water, so they are fluid. The slight diuretic effect of the caffeine in the drink does not “offset” all the water that is in it. We will come back to this one in a minute.

Note that I’m not talking here about small drinks with loads of caffeine, like a triple Expresso or a can of Red Bull. I’m talking about the kind of coffee, or soft drink, that most people drink. My standard cup of coffee is about 275 ml, which would take a fair bit of peeing out.

“If your urine looks dark, you are dehydrated”

Not true. It would be more accurately to say that “pale yellow” or “almost clear” wee (which the Hydrationistas tell you you should look for) means you have water –loaded yourself (i.e. you have drunk loads extra) and thus are peeing out unusually extra dilute stuff.

“When you start to feel thirsty, that means you are already dehydrated”

Not true. Your body detects tiny changes in “body water” very well. To put it more precisely, the body detects how concentrated your body fluids are, that is, their “osmolarity”, and a change of 2% is detected easily. The body then tells you to correct this small change by drinking more and peeing less out. The wonders of evolution. Anyway, the system is both incredibly sensitive, and fast. So you get thirsty because it is time for you to have a drink, but NOT because you are dehydrated.

[Dehydrated is what you will get if you start feeling thirsty and then drink nothing for the next several hrs. Dehydration is usually taken to mean that your body osmolarity has risen by 5% or more. So you get thirsty, and drink, without ever being close to being dehydrated.]

– and finally, one Valtin doesn’t discuss in precisely this form, but which has recently turned up in the literature for “Brain Gym” (comprehensively trashed by Ben Goldacre here).

“Liquids (other than water) are processed in the body as food, and do not serve the body’s water needs.”

Again not true, and total scientific nonsense. Common sense should tell you that a bit of dissolved sugar does not stop water being water. So the other fluids count. And so does water in what you eat, roughly a litre a day of it, see below.

Being charitable, this statement COULD have its origins in the fact that there is a bit of evidence, which Valtin discusses, that taking more fluids along with your meals might promote satiety (feeling full). Therefore one could hypothesize that consuming foods with high water content might make you feel fuller (all else being equal, which it rarely would be, so that all other satiety cues were the same).

Anyway, this might mean that it is a good idea to drink something with your meal (which most people do anyway, of course) since it could help moderate how much you eat.

I can just about see how, if you were a bit confused, you might interpret this as “that water in what you ate was processed as food” and hence didn’t count as water. You would be totally wrong, though. Of course, your confusion suits the Hydrationistas perfectly.


Back to your Daily FLUID (not water) intake

Your total water requirement is “filled” by the fluids you take in over the courses of a day. Some of that water is in your food, depending in amount on what food you eat – a general value that appears widely in physiology textbooks, as we already noted, is that you get about a litre of water this way. It depends on exactly what food – it wouldn’t take a genius to work out that grapes, or watermelon, or soft fruit generally, is mostly water. But all food contains water. The milk you put on your cereal (if you do) contains water. And so on, and so on.

If humans needed clear fluid above and beyond “other water intake”, then breast-fed new-born babies would all be dying of dehydration.

By now it should be abundantly clear that, if you take a quantitative look, a large part of the daily “drinking requirement” will be met by drinks OTHER than water. Hence all those family stories about “Grandpa Albert never drank water, only tea”. Valtin gives an example of a day’s intake from himself:

Representative daily fluid intake of H Valtin recorded on 29th Aug 01

Breakfast coffee with milk 650

Orange juice 175

Lunch cranberry juice 240

Dinner cocktail 125

Water 250

Total fluid intake 1,440 ml

And here, for comparison, is mine, from last Sunday:

Representative daily fluid intake by the author recorded on Feb 17th 08

Breakfast Coffee with milk 550

Lunch Diluted apple juice 325

Coffee 275

Dinner White wine 300

Water 350

Total fluid intake 1,800 ml

These amounts match well to the widely-recognised daily fluid requirement of a standard human, that being typically summarized in physiology textbooks as “the 70 kg man”. Valtin summarizes various measurements of daily fluid intake, all of which tell you about the same thing – your daily drinking requirement, assuming you eat an average sort of diet, is probably 1.2-1.7 litres, give or take. Inter-person variability will mean a range of values.

Another thing you can measure easily is the amount you wee out in 24 hrs. This will be balanced, very approximately, by your intake. Again, Valtin summarizes the studies that suggest that average daily urine output is around 1.7 litres (1700 ml). The similarity of this to the fluid intake is clear.

The above is slightly simplified since, remember, there are there are other ways you gain and lose water. But the clear take-home message is that your body’s fluid balance system turns over nice and happily if you drink about 1.5 litres (1500 ml) or liquids (all of them), and wee out something slightly more. And if the mean fluid intake value is about 1500 ml, then anything between 1200 and 1800 might be right for you. Humans, after all, are not all the same.

But to feel you have to sluice down nearly two litres of water, as well as whatever else you drink a day – give me a break.

But we KNOW all that extra glugging is good for us! You can’t prove it isn’t!

Of course, some of the Hydrationistas insist they have an answer to this. They cannot really dispute the scientific body of evidence, as so masterfully summarised by Valtin. Instead, they simply claim it is all irrelevant, as there is no trial to show that drinking loads of extra water ISN’T good for you.

Dr John Briffa exemplifies this approach. A couple of months ago he discussed this issue on his blog, prompted by an article in the Christmas 2007 issue of the British Medical Journal that debunked several “health myths” including “drink eight glasses of water a day”.

“Absence of evidence”, intoned Dr B in one of his favourite lines, “is not evidence of absence”.

And other Hydrationistas take similar lines. That standard intake (around 2-2.5 litres by all routes, including food, or 1.5 litres of fluid) is simply that needed to avoid dehydration, they say. But it is healthier to drink lots more.

Note that they give no evidence for why this should be true – because there isn’t any. As Valtin clearly sets out, if you are a normal human individual, and you take more water in, your homeostatic system will rapidly adjust and pee more out. That is what your body has evolved to do. The extra flushing will mean more trips to the toilet, and considerable wallet-lightening if you are a bottled water enthusiast. But it won’t make you healthier.



And… absence of what kind of evidence?

Ah, say Dr Briffa and the other Hydrationistas, how do you know that? There is no rigorous clinical trial that says so!

Now this is an interesting general point, because it relates to a wider question about “Alt Health modalities”.

Is it really necessary to run complex, and expensive, large modern trials to demonstrate something is useless, when there is 50+ years worth of scientific and medical evidence, extensively tested, re-tested, critiqued and reviewed, showing that the theories on which the idea is based have zero validity?

In the water context, there is not a scintilla of scientific or medical evidence giving any grounds for the idea that super-slurping water will make you “better than well”

On the contrary, to repeat it for the umpteenth time in this piece, there is shed-loads of evidence that around 1.5 litres a day of LIQUID, plus what is in your food, is what your body has evolved to be happy with. And furthermore, that your body will “adjust” your thirst to get you to drink just that.

In statistical terms, what we would say is that the “prior probability” of the Hydrationistas’ view – “drinking lots of extra water, over and above what your body actually requires, is good for you” – being true is extremely low.

So under these circumstances, why spend millions (and it would be millions) running a trial to try and show that extra water drinking has health benefits?

Or put another way, on whom should any “burden of proof” lie for the idea that drinking an extra litre of water a day is “healthy”?

On the scientific and medical mainstream?

I don’t think so. The burden of proof clearly lies with the Hydrationistas. It is not the job of mainstream medicine and science to have to keep proving what is already brain-achingly obvious, and supported by all the science, simply because the Alt-ies find it convenient to say “No fair! No evidence!”

And it’s not as if there’s no money in water for anyone who could prove super-slurping made you “better than well”. Bottled water is a global mega-industry, with a market worth something close to a staggering Two Billion pounds a year in the UK alone. Plenty of potential funding there for some enterprising Hydrationista to run a proper study to demonstrate the benefits of super-consumption of bottled water.

Indeed, when he wrote his review five years ago, Heinz Valtin said exactly this.

“In view of the strong suggestive evidence cited [that people don’t need 8 glasses of water a day]… I would argue further that… the burden of proof that everyone needs 8 × 8 should fall on those who persist in advocating the high fluid intake without… any scientific support.”


And a bit later:


“Having found no evidence in support of 8 × 8 has placed me in the awkward position of having to prove a negative. I hope, therefore, that anyone who knows of contrary scientific evidence will bring it to my attention.”


Five years later, Valtin, and the rest of us, are still waiting. From which you can draw your own conclusions.



Drinking water – or bathing in it – can be deadly (not) – part 2 The men in grey suits… are actually on the case

Drinking water – or bathing in it – can be deadly (not)







29 Responses to “Glug glug glug … why those eight glasses a day don’t HAVE to be water (or eight).”

  1. emily Says:

    This one drives me crazy. The liquid need not even be free liquid in a glass. We can get rather a lot of it from squishy foods like fruits and veges too.

    Oh, Oh, next can you do ‘we only use 10% of our brains’? Amazing how many otherwise fairly normal people parrot that one….

  2. draust Says:

    I think someone’s already got there before me on the “10% of our brain” Myth, Emily! See e.g.

    …and here’s one by noted skeptic (and genuine neurologist / neuroscientist) Steve Novella:

  3. draust Says:

    Agree about the fruit ‘n’ veg too – that was why I mentioned watermelon, but perhaps I should have plugged it a bit harder. There are certainly people who would say that, if you eat lots of fresh fruit and veg, you need less daily fluid intake, down to a litre a day or even less.

    I think what a lot of the public don’t get is that the body homeostatic systems essentially mean that it is quite difficult to get dehydrated unless some condition is specifically “unusual”, e.g. walk miles in 90 degree heat, feel thirsty but don’t drink for hours and hours, and so on.

    I suspect many of the water-super-gluggers – at least the ones doing it as part of an Alt Health kick – will also be keen fruit ‘n’ veg eaters, so their total daily fluid intake must be huge. I wonder how many times a day they have to void their bladders? I always suspect such folk must produce prodigious quantities of the other main *waste product* too, but interestingly Valtin refers to a study where upping water intake by a litre a day didn’t increase “stool output”.

    Physiology does take one into such tasteful areas…

  4. gimpy Says:

    QUality post.

    I wonder how many times a day they have to void their bladders?

    Is there any research on this? I have to confess I do tend to drink quite a lot of (tap) water during a day as well as being a keen fruit & veg man. Now I’m probably a six a day man when it comes to bladder release (and young enough not to have prostate problems) but a 0.75 a day man on the stool front. Is this typical?

    Feel free not to answer.

  5. Dr Grumble Says:

    It’s amazing how people have been persuaded to pay more for water than they do for petrol. Even the children of people who can see the madness of this have been taken in. Somebody is making a lot of money from our stupidity.

  6. draust Says:

    Gimpy – You sound reassuringly normal to me, though I can’t pretend to any special expertise beyond what one reads in the physiology textbooks or online – “6-7 times / day, give or take” is a phrase that seems to ring true-ish. To compare yourself with a recent study on “voiding frequency” in men, if you’re into that sort of thing, see e.g. here.

    On the stool front, the range of “normal frequency” is said to be wide – I understood the received wisdom to be that anything between 3/wk and 3/day was considered normal, with 1/day being the median . Again, stress I am not an expert in this area, though I can proudly boast that I once wrote a paper in that most evocatively titled journal “Gut”.

    Dr Grumble – Welcome to the blog – I couldn’t agree more. You put it so well on the Witchdoctor’s blog post you gave the link to that I had been thinking of reprinting your comments if I do a final Anti-Hydrationista Counterblast. It is fascinating how the “public conversation” now finally seems to be turning back the other way after years of water-promotion, but this time with the accent on bottled water’s “non-sustainability” or wastefulness.

    General PS – For anyone who is interested, an amusing account of a distinguished British physician, nephrologist and researcher doing heroic water drinking (and other) experiments on himself (and friends) can be found here (PDF).

  7. gimpy Says:

    That de Wardener article is quite wonderful. Thank you for bringing my attention to it. Sadly such self-experimentation is rather discouraged these days although some friends of mine did have fun measuring the effects of alcohol on the ability to win at poker using a breathlyser and pack of cards. Sadly they forgot the control group.

  8. What could be so fine… as to be alkaline (Warning: Irony) « Dr Aust’s Spleen Says:

    […] Dr Aust’s Spleen A grumpy scientist writes « Glug glug glug … why those eight glasses a day don’t HAVE to be water (or eight). […]

  9. LeeT Says:

    Don’t forget good ole milk as a source of fluid.

    My own conspiracy theory is that the AltMed lobby don’t like milk as if we stop drinking it and also stop eating dairy products such as cheese we will become deficient in calcium. Then we will have to buy lots of expensive mineral supplements to solve the problem they caused in the first place. Cheeky so-and-sos.

  10. draust Says:

    Interesting idea, Lee. The AltMed lobby do seem to have a rather vexed relationship with dairy products, which they routinely warn you off as they will “clog your arteries” or activate your (usually mythical) “dairy intolerance”.

    The problems of getting enough calcium tend to be greater for women, who also have frequently been sold the idea that dairy products will make them fat and are thus to be shunned.

    There actually IS a bit of calcium in tap or bottled water. How much depends on where you live, if it’s tap water, and what brand you drink, if it’s bottled. Some of the bottled mineral waters have surprisingly large amounts of calcium in them. My dad drinks this one in France, which contains about 5 mM Ca2+. I don’t care for the stuff myself as it leaves me still feeling thirsty.

    Calcium supplements have been getting a bad press recently, even in the people (post-menopausal women with worries about loss of bone density) for whom they are mostly prescribed.

    As ever, if you were thinking you need a bit more of something, it seems to be better to start by eating more of the common-or-garden dietary things that have whatever-it-is in them than to rush down to Tesco or Boots for some supplement tablets. I find myself saying this so often with regard to dietary stuff that it is becoming something of a mantra. Fortunately my 70 yr-old mother likes a good cheese, and takes her tea and coffee with milk.

  11. silencer Says:

    Obviously if one drank wine and ONLY wine, they would not be long for this world. Kidney failure would be sudden and dramatic.

    Urine should be mostly clear. Try doing that with any other liquid or diuretics like coffee.

    You are going to injure people with your “scientific” advice.

  12. casual Says:

    Have you guys seen the discussion over this post at Reddit? It’s bloody hilarious!

  13. casual Says:

    sorry, I should have linked: here it is

  14. Nash Says:


    Up until the late Victorian era, people drank fruit juices, green tea, beer and wine all the time. Drinking water was dangerous, especially in cities.

    “Urine should be mostly clear.” Mine is yellow and stinks of piss, and I’m perfectly healthy.

    After exercise drink fruit juice rather than water. You will be amazed at how much better you will feel.

  15. draust Says:

    Quite so, Nash. In pre-modern times, once people lived in sizeable cities, drinking water was something only the very poor did, since the water was commonly not very clean. In medieval times beer was an important part of the diet, taken (in Northern Europe particularly) at all meals – and that includes breakfast. Many families brewed their own, and those that didn’t could buy it, or trade for it, from those that did.

    We are, of course, lucky that water sanitation since the late 19th century has allowed us clean water to drink. Another rather useful scientific achievement.

    What I find bizarre about the Reddit thread Casual linked to is that some people clearly can’t get their heads round the idea that fruit juice, beer, coffee, tea and even wine are mostly water. Whoever “Silencer” is, he clearly didn’t get much of a science education. A strong modern 5% beer is 95% water by volume, or (for hardened chemists) about 40 Molar water.

    As for coffee.. you put water in a coffee pot, and a liquid comes out the other end. Duh. It is not magically transformed by alchemy into something other than water, as in good old H2O molecules. What you have is a solution of chemicals – natural ones – from coffee beans in water

    Incidentally, even the mineral waters favoured by the Hydrationistas contain some dissolved salts, so the idea that you must drink “pure water with absolutely nothing else in it” is not even self-consistent within their own Alt.Reality.

    And the “clear urine” line is, as explained in the post, a line (and no more) that the Alt Med hucksters use to convince you that you are normally dehydrated, which you aren’t. The point of the post was to counter the endless fear-nonsense put out by Alt Med idiots about how you MUST drink 2 litres of clear water regardless of what you already drink each day.

    The take-home advice?

    “Drink fluids normally” – carry on drinking all those different drinks you drink during a normal day, and don’t worry. If you do feel thirsty, drink a bit more fluid.

    Now, just how hard is that to understand?

  16. Ephistopeles Says:

    Hmm… I bet I had bought only souls!
    But there’s impression that they sell their brains together with souls…

  17. Nash Says:

    Considering the amount of booze consumed by our ancestors on a regular basis I wonder how many important decisions were made whilst those taking them were half-cut?

  18. Nash Says:

    Another factor to consider in liquid intake is temperature and levels of extertion. The 2 litres of water sounds fine for being in the Sahara, but in the Artic this would be too much.

    For instance during the summer I needed much more to drink after a run than I did this evening. Fruit juice is better than water in that it restores minerals, salts and suger levels much better than water on its own.

  19. Claire Says:

    A homeopath in Houston doesn’t want to die from drinking tap water. Cheeringly, it looks as if not many of her fellow Houstonians (?) agree with her.

  20. draust Says:

    Yes, thanks for that link, Claire. A sensible article exploring many of the aspects of the bottled water / health / lifestyle question. Would that we had had more articles like that in the UK, rather than the endless “drink lots of water – sip at all times!” line peddled almost as a reflex by virtually every health / lifestyle article you have read in the UK papers over the last decade.

    It seems clear that a combination of harder times financially, and the desire to be more eco-friendly, is cutting into the sales of bottled water. The US article does make one quite interesting point, arguing that bottled water drinkers can be subdivided into those drinking bottled water instead of tap water, and those drinking bottled water instead of a soft (carbonated fizzy) drink. I have certainly been in the latter category myself on and off over the years, though I am now making an effort to drink tap water rather than overpriced fizzy mineral.

    I had to laugh to see the homeopath at the beginning of the article described as a “homeopathic doctor”. While this could be an accurate description of a proper medical doctor (MD in the US or MBBS / MBChB in the UK) who also practises homeopathy – though I would pedantically prefer to see such people described in exactly those terms to avoid confusion – I suspect it is far more likely she has some kind of “naturopathic doctor” qualification (ND in the US). Anyone who goes to such a person believing them to be a doctor is in for a nasty shock. If they are lucky it will only be to their wallet. If they are unlucky it could be much worse.

    Later note: a quick Google reveals this is correct – the quoted person is indeed an “ND”. The web profile has some of the characteristic language that should make anyone half sane run a mile:

    It is my belief that all DIS-EASE is caused by imbalances in the body. It is my goal to help you restore balance and therefore, HEALTH. I consult on a variety of conditions including, environmental toxicity, autoimmunity, allergies, autism…


    …yada yada yada.

    The first sentence is key. It is one of those “Scopies’s Law”-style rules that whenever anyone writes disease as “Dis-Ease”, as if this was some profound insight, then they are a card-carrying Alt.Reality whackjob. Ditto for the phrase “imbalances in the body”, which is probably enough for a “Quackometer” score of five canards all on its own.

  21. Claire Says:

    “the quoted person is indeed an “ND”. ”

    And, inevitably, lists her specialist ‘strengths’ as, what else, allergies and asthma. Grr. One can only hope she’s not as cavalier as this naturopath .

  22. Nash Says:

    Today one of my work colleagues came out with the ‘you can’t use the plastic bottles that drinking water comes in, more than 3 or 4 times, after that the plastic becomes poisonous.” urban myth.

    I informed him that the water I was drinking was ‘Bathroom Tap’ and the bottle was nearly 2 years old.

    Another colleague posited that the only issue in re-using bottles was one of hygiene. As long as you clean them out there is no reason why you shouldn’t use them for years.

  23. Svetlana Says:

  24. Journey through a Burning Mind » Stuff from the Science Blogosphere Says:

    […] Aust provides an excellent post on why the common myth “you need 8 glasses of *water* per day” is exactly that: a myth. […]

  25. Chris Aylmer Says:

    Brilliant article. I am sick of hearing about how much water we are supposed to drink. Plastic bottles of water pollute the environment now. You get the feeling that parents and teachers should feel guilty and could be censured for not supplying children with enough water during sporting activities etc., in case they become dehydrated. Nearly everyone seems to buy into this ridiculous theory. Millions of years of evolution have developed a very efficient method of balancing water intake/output and thirst in all living creatures including humans, but we are told the body is somehow unaware of dehydration until it is too late! I’m not sure it’s all about the evil water bottle industry though. I think it’s just one of those stupid ideas that people buy into. The cosmetic industry may be more to blame here. I remember repeated articles about the skin condition and complexion supposedly improving in women when the body is “fully hydrated” with water. Thus the idea of topping up with water all day long may be something to do with vanity as well as water sales.

  26. Vorobyey Says:

    I have been talking to a lot of blank walls around me about this for years.
    I just get looked at as an utter idiot by them (fortunately not all my friends are this naive), but I can’t point them in the direction of anything vaguely scientific ‘cos “It’s too hard”. I will try them with this post.

  27. draust Says:

    Vorobyey – thanks for commenting.

    It can be a bit of a thankless task trying to inject some realism into many people’s thinking about this… as the recent post highlighting some of the other “water stuff” I have written indicated.

    Anyway, if this post helps at all – and it has actually been signposted once or twice on forums when “hydration” was being discussed – it would be very pleasing.

  28. followthelemur Says:

    *wonders off and pours another cup of tea*

  29. A Snacking Craze « Follow the Lemur Says:

    […] I have a minor issue with the drink more water point, merely because it harks back to the “drink 8 glasses of water a day” myth. […]

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