Water glasses - Waterlogged. 8 Glasses Of Water Per Day Debunked.

Waterlogged. 8 Glasses Of Water Per Day Debunked.

Water glasses 300x162 - Waterlogged. 8 Glasses Of Water Per Day Debunked.


It’s time I bust this one wide open.


Of all the nutritional myths out there, this one has got to be a contender for the ‘Mother of All Myths’


“Drink 8 to 10 glasses of water each day ” is HORRIBLE advice.


The question is why? The human body needs water to function; we can only live for 2 to 3 days without ANY water at all.


So what’s the problem?

Water. The miracle nutrient

Unless you’ve been living under a rock, you’ve been bombarded with messages like you need to drink 8 to 10 cups of water per day‘.


Another favourite of mine you need to drink half your weight (pounds) in ounces of water every day‘.


Since I’m 160 pounds, that translates to 80 ounces, or ten, 8 ounce glasses of water.


My back teeth are floating just thinking about it.


The reasons are as endless as they are spectacular, and in some cases, down right magical.

  • Your brain is made of water and drinking more water will help you to think more clearly
  • Drinking lots of water removes toxins from your body
  • If you don’t drink enough water, your liver becomes over-taxed and cannot metabolize fat
  • Not thirsty? That is the first sign of dehydration; if you wait till you’re thirsty, it’s too late
  • Drinking water will give you glowing, dewy and supple skin
  • 1 cup, or mug, of a caffeine containing beverage (coffee/tea) results in loss of 2 cups of water from the body
  • Drinking water will help you to burn more fat


Self-stylized ‘health experts’, as I like to refer to them, LOVE to throw around nuggets like these and think that they’re actually giving nutrition advice.


Hey, these sound-bytes are catchy, easy to tweet or post on Facebook, and to the unsuspecting person, ‘make sense???’.


In all fairness, there’s a speck of truth behind most myths; but the key word is ‘speck’.


As a formally educated and trained professional, I’m more interested in evidence, a.k.a. proof.


Anyone making claims like the ones above should be able to back up, or substantiate, those claims with research etc. To date, I’ve yet to see any robust data, or studies, to support these assertions. Anyone?


Trying to present dogma as fact, or simply parroting a message isn’t good enough. I expect much more, and so should you.


dogma (noun): an authoritative principle, belief, or statement of ideas or opinions, especially considered to be absolutely true


parroting (verb): one who imitates the words or actions of another, especially without understanding them


Water pouring 300x200 - Waterlogged. 8 Glasses Of Water Per Day Debunked.


Fluid balance

To better understand how much water we really need, a basic understanding of fluid balance, or how the body ensures that the amount of water leaving the body is equal to the amount taken in, is needed.


Obviously individual water requirements vary to some degree depending on on the size of the person, amount of physical activity/exercise, environmental temperature and humidity. I’m not disputing that, what I am disputing is the notion that we need to consume 8 to 10 glasses of added/extra water per day under normal resting conditions.


Fluid balance = amount of fluids in – amount of fluids out [to maintain an individual’s total body water content]

How much water do we REALLY need?

According to real research, and not just someone else’s opinion, or what another blogger states, or what you read in one of those free magazines from the health food store says, our fluid/water requirements are based on:



To replace losses, a constant supply of water is needed which we get from:

  • Food, which is typically 40-90% water by weight [500 ml – 1000 ml, or 2 – 4 cups, per day]
  • Added fluids like water, tea, coffee, soups, juices [1200 ml, or about 6 cups, per day]
  • Aerobic respiration, or ‘metabolism’; water is a by-product of our biochemical processes [300 ml, or just over 1 cup, per day]


This comes to a total of 2000 ml (2 litres) to 2500 ml (2.5 litres) or about 8 to 10 cups  per day, give or take.



Water is lost through normal physiological activities:

  • respiration (breathing) and perspiration [we lose about 500 ml to 650 ml, or just over 2 cups, per day]
  • urination [we lose another 1500 ml, or 6 cups on average per day; more if you drink more, less if you drink less], even feces [100 ml, or just under 1/2  a cup]


This comes to a total of 2200 ml (2.2 litres) to 2600 ml (2.6 L)  or about 8 1/2 to 10 cups per day, give or take.


In a word: balanced


So why would anyone suggest drinking copious amounts of extra water than what is needed to maintain fluid balance?


Water drinking 300x200 - Waterlogged. 8 Glasses Of Water Per Day Debunked.


What about those claims?

Drinking water helps you to think more clearly

Provided you are meeting your fluid requirements and fluids in = fluids out, drinking more water than is physiologically needed will not boost brain power or increase mental clarity. 


This is not to be confused with genuine dehydration (excess water loss due to excessive, difficult to manage, vomiting or diarrhea, or due to excessive sweating where fluid replacement isn’t happening, i.e. unable to respond to normal thirst cues).


Where are the randomized controlled trials to prove this claim? Note, feeling thirsty DOES NOT mean you’re dehydrated, it means you’re thirsty, so respond appropriately.

Caffeine will dry you out like a prune

Caffeine containing beverages are dehydrating, or so ‘they’ say. Now that you know what true dehydration is, and is not, this claim should be self-evident. The reality is this; the kidneys are supreme at regulating fluid balance. In fact, it’s one of their primary roles.


With the exception of pharmaceutical diuretics, there isn’t much we can do, under reasonable circumstances, to manipulate the kidney’s ability to do their job of maintaining fluid balance; any tiny increase in urine production via caffeine will simply be managed by the kidneys; they’ll filter less water.


This myth just doesn’t hold any water as explained here, in one of many reviews.

You need lots of water for dewy skin

Our skin does not, and will not, plump up after drinking water like my poor tomato plants do if I’ve neglected them on a hot summer’s day.


The quality of skin is largely genetic; yes proper exfoliation, good basic nutrition and avoidance of excessive alcohol, harsh winds, dry heat and smoking will ensure you’re glowing at your best but drinking more water does nothing – again – where’s the evidence? The skin you see is literally dead, on its way out as new cells are formed and push their way to the surface. 


The skin’s natural moisture level fluctuates depending on what your skin’s protective lipid (fat) layer is exposed to. This lipid layer helps keep moisture in and germs and irritants out. (That’s why dry skin can become red and itchy).


Moisturizers help to keep moisture from evapourating which is good, and will smooth out any dryness, but 8 glasses of water a day won’t change this. Sorry.

Peeing all day long = lots of toxin removal

Drink lots of water and you’ll make lots of pee; watery pee.


Because the minerals and electrolytes in your blood have to be regulated, and maintained, in a narrow range (to prevent, for one, low blood sodium, or hyponatremia; seizures anyone?) the body will decrease the release of the anti-diuretic hormone (ADH), the kidneys will respond by selectively getting rid of the extra water, in other words, they won’t reabsorb it.


Urinalysis testing has confirmed that it’s mostly water and not extra toxins.

Drinking water makes you burn fat

Show me a randomized controlled trial whereby the metabolic rates, confirmed by the gold standard; indirect calorimetry, of two groups of people, consuming different amounts of water, have been compared.


A study that has shown an increase in fat oxidation (as reflected by a respiratory quotient of 0.7) in those subjects who consumed more water than a group who didn’t; and who consumed more water than is needed to maintain fluid balance.


Listen, if there is such a study, even one, I’ll be the first to shout it from the roof tops. 

If you’re thirsty, it’s too late, you’re dehydrated

Did I miss the memo that said we’re going to use thirst and dehydration interchangeably?


If you’re thirsty, it’s time to consume some fluids (a beverage will be absorbed more quickly than food, but any source will help); listen to your body and respond appropriately.


Saying that you’re dehydrated because you’re thirsty is like saying you’re malnourished/suffering from starvation because you’re hungry. Anyway…ever notice how animals drink to thirst and eat to hunger?


For some reason we think that humans are the exception; that we need to follow a bunch of rules when it comes to eating and drinking. Again, I want proof that someone who feels thirsty is dehydrated, again for reference, here’s true dehydration explained.


In Part 2 of this post, I’ll review some of the historical context which led to this blindly accepted ‘truth’ in nutrition and explore the potential negative effects of consuming too much water.


Doug Cook RDN is a Toronto based integrative and functional nutritionist and dietitian with a focus on digestive, gut, mental health.  Follow me on FacebookInstagram and Twitter.


  1. Gardner EJ, Ruxton CHS, Leeds AR. Black tea – helpful or harmful? A review of the evidence. Eur J Clin Nutr. 2006;61(1):3-18. https://www.ncbi.nlm.nih.gov/pubmed/16855537 
  2. Grandjean AC, Reimers KJ, Bannick KE, Haven MC. The effect of caffeinated, non-caffeinated, caloric and non-caloric beverages on hydration. J Am Coll Nutr. 2000;19(5):591-600 https://www.ncbi.nlm.nih.gov/pubmed/11022872
  3. Heinz, V. “Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8 × 8”?  American Journal of Physiology – Regulatory, Integrative and Comparative Physiology Published 1 November 2002Vol. 283 no. R993-R1004. http://citeseerx.ist.psu.edu/viewdoc/download?doi=
  4. Paque, C. Water consumption in Saharan nomads. A remarkably reduced and constant consumption. Nouv Presse Med. 176;5(32):2087-90. https://www.ncbi.nlm.nih.gov/pubmed/980741
  5. Maughan RJ, Griffin J. Caffeine ingestion and fluid balance: a review. J Hum Nutr Diet. 2003;16(6):411-20. https://www.ncbi.nlm.nih.gov/pubmed/19774754
  6. McCartney M. Waterlogged? BMJ.2011;343:d4280. PubMed PMID:2175074. https://www.ncbi.nlm.nih.gov/pubmed/21750074
  7. Walter F., PhD. Boron (2005). Medical Physiology: A Cellular And Molecular Approach. Elsevier/Saunders. ISBN 1-4160-2328-3. Page 829. https://trove.nla.gov.au/work/12168683
  8. Whorton JA. Nature Cures: The History of Alternative Medicine in America New York (NY): Oxford University Press:2002. https://www.amazon.ca/Nature-Cures-History-Alternative-Medicine/dp/0195171624


Photo credit: Emil magnusson

Comments 9

  1. Mike
    April 25, 2017

    What are you going on about? Who says you drink 8-10 glasses beyond the 8-10 glasses you need to hit balanced input and output? This is just another lazy, click baity article where you actually prove the myth you’re trying to debunk. I hope you’re proud of yourself.

    1. Doug Cook
      April 25, 2017

      Who says we need 8 to 10 glass of ADDITIONAL water? lots of people, and those messages are all around, just need to look for them and of course, anyone who works in the health field, gets this question all the time…

  2. Thecead.Com
    February 24, 2020

    And yet every summer we are inundated with news media reports warning that dehydration is dangerous and also ubiquitous .

    1. Doug Cook RDN MHSc
      February 24, 2020

      Sigh. As I mention in the posts, there are times when our water loss can outpace our thrist cue and yes, when it’s super hot dehydration is a possibility but if it was that crucial, to guzzle water and not rely on one of the most primative instincts for survival (thirst), the human race would have gone extinct eons ago

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