Why drink water, and how much is enough?

Like a lot of people working in the nutritional field, I believe maintaining hydration is important for peak wellbeing and health. Water makes up about two-thirds of the body, and therefore has the potential to play a critical role in just about any bodily process one cares to mention. Like what? Well, now the benefits of hydration (and the perils of dehydration) have been documented in a review in this month’s edition of the European Journal of Clinical Nutrition [1].

One of the two authors of this review is from the Department of Physiology at the University of Lausanne in Switzerland. The other author’s place of work is listed as ‘Nestle Waters’ in Paris, France. Oddly, though, the fact that one of the authors works for a company selling bottled water is not declared as a conflict of interest. Ho hum, onto the review…

To my mind, the review actually does a very good job of summarising the role that water plays in the structure and function of the body. Here’s a summary:

Water as a building material
Water is present in each and every cell in the body, and acts first as a building material.

Water as a solvent
For nutrients like glucose and amino acids.

Water as a carrier
For the transport of nutrients to cells, and the removal of waste from those cells. Also, for maintenance of blood volume and circulation, which is essential for the function of all organs and tissues of the body.

Water and thermoregulation
To allow sweating, which can dissipate heat from the body.

Water as a lubricant and shock absorber

Water ensures lubrication for joints, as well as parts of the body including the mouth, digestive tract and lungs.

In terms of the effects signs of dehydration, the review lists (for mild-to-moderate dehydration) among other things:

Dry, sticky mouth
Sleepiness or tiredness
Decreased urine output
Muscle weakness
Dizziness or light-headedness

The review goes on to cite official recommendations regarding water requirements (European Food Safety Authority, 2008). These come out at about 1.5 litres a day for adults, with more required during pregnancy and for breast-feeding mums. However, the authors also allude to the fact that making blanket recommendations is not easy, because needs for water will depend on several factors including climate and physical activity.

The authors also write about the assessment of hydration status, and mention urine colour as an indicator. I generally suggest to individuals that this is the most practical way of gauging hydration status. The usual advice I give to individuals is to drink enough water to ensure that the urine is pale yellow throughout the course of the day. I might follow this up with something like “If at any time you notice your urine has straying into darker tones, and has become noticeably odourous, the chances are you are dehydrated and you might think about increasing your water consumption.”

I don’t think anyone’s formally studied this, but my overwhelming experience in practice is that individuals who take steps to improve their hydration almost always feel improvements in terms of their energy and wellbeing. Maintaining hydration easily is generally facilitated by ensuring that you have water by you. So, keep a bottle or jug of water and a glass by you at work, in the garden, when relaxing etc. Most individuals find themselves quite naturally reaching for water as long as it’s in front of them.


1. Jequier E, et al. Water as an essential nutrient: the physiological basis of hydration. Eur J Clin Nutr 2010;64:115-123

, , , , , , ,

19 Responses to Why drink water, and how much is enough?

  1. Bill Davis 11 February 2010 at 3:21 pm #

    What about if you are taking a vitamin B supplement?

  2. Tim 11 February 2010 at 7:04 pm #

    This is excellent. It really doesn’t help if you have a weak bladder and you’re out and about though 🙁

  3. Dr John Briffa 12 February 2010 at 3:10 am #


    It’s harder to gauge state of hydration from urine colour when taking a B-complex supplement, as B2 (I think) makes the urine colour more yellow. However, I still encourage individuals to monitor the intensity of the colour, as well as smell, to keep a handle on their hydration. Another thing to keep an eye on is frequency of urination. Assuming normal bladder capacity, if someone goes for several hours without urinating, chances are their not drinking enough water.


    Weak of ‘irritable’ bladders are often helped with magnesium supplementation (in both men and women). You might want to have a look around the site and elsewhere for more information on this.

  4. Rizwan Sayed 12 February 2010 at 11:11 am #

    Does drinking tea, coffee, juices constitute “water” and part of the 1.5 litre daily target?

  5. Esther 12 February 2010 at 11:37 am #

    Thanks Dr. B.

    Dr. F. Batmanghelidj has done a lot of research regarding water, he has written books such as “Your body’s many cries for water”, and his website is http://www.watercure.com

    Very useful for further information on the subject. 🙂

  6. Angie 12 February 2010 at 11:43 am #

    Yes, B2 can make it bright orange – depending on how much you need, and therefore absorb. The more it is excreted, the darker the colour.

  7. Sue 12 February 2010 at 12:25 pm #

    “Does drinking tea, coffee, juices constitute “water” and part of the 1.5 litre daily target”

    I wouldn’t think so considering tea and coffee contain caffeine and are dehydrating. Perhaps juice but its best to have water.

  8. Edward 12 February 2010 at 1:35 pm #

    I seem to recall reading a study about quantity of water to drink that said part of the daily requirement was taken in via vegetables and other foddstuffs – another factor in making it hard to lay down solid guidelines.

    Also, even though tea and coffee are mild diuretics and so promote fluid loss, I think they could count as part of the intake so long as output equals input. This is another hard question.

    Overall I reckon Dr B’s advice is good: make sure you drink enough water to urinate frequently and to keep the colour looking right. However this doesn’t mean that you need to carry a 500ml bottle of water with you on a 5 minute train journey in February (as I see everyday in London) – you are not going to dehydrate or die of thirst over that space of time. 🙂

  9. Hana 12 February 2010 at 3:36 pm #

    Referring back to vitamin D- I have severe fibromyalgia,and after discussing your blogs on Vit D with my GP, he agreed to test for Vit D- the result came back to-day-” 95-within normal range-no action required” cannot find anywhere how to translate this into your measurements in ng/ml or mmml/l
    I find your blogs very interesting.

  10. Malcolm 12 February 2010 at 3:44 pm #

    I think the diuretic effects of tea and coffee are greatly exaggerated. I read recently that if you ate the dried leaves or beans they would have a mild diuretic effect, but if drunk as beverages there is a net fluid gain.

  11. Dr John Briffa 12 February 2010 at 4:41 pm #


    ’95’ is probably mmol/l but, obviously, I can’t be sure. To convert mmol/l to ng/ml divide by 2.5 (95 mmol/l comes out at 38 ng/ml). Thanks for your kind words.

  12. TimT 12 February 2010 at 4:48 pm #

    But if we are water deficient, why don’t we get thirsty? I rarely get thirsty, but I drink a few glasses of water a day anyway. I always have a rather dark urine. Does the dark urine imply that I’m dehydrated even though I’m not thirsty or might there be other causes of dark urine like secretion of minerals and other stuff?

  13. Valerie 12 February 2010 at 6:20 pm #

    I consider it a huge conflict of interest that the writers work for a bottled water company. I have had times in my life where I conscientiously tried to get those mythical 8 glasses a day. I drank 1 L by lunchtime. I was always thirsty. It became an addiction. I took an anthropology class in college. I wondered how much water our paleolithic ancestors drank. Replacing soda and juice with water is very healthy. Just like everything else, listen to your body. Drink water to thirst.

  14. Dr John Briffa 12 February 2010 at 7:56 pm #


    One potential problem with using thirst as the primary driver of water-drinking is that low-level dehydration might not provoke thirst but still may be significant enough to affect health and well-being. Also, some people (particularly the elderly) have very ‘blunted’ thirst responses and can therefore be very dehydrated before they get thirsty.

  15. jon w 12 February 2010 at 10:01 pm #

    I have noticed when eating a high fat / low carb diet, there is much less need for water. a cup of coffee in the morning, some vegetables and meat with sauce, and I easily go all day without being thirsty on a typical day of sitting in the office and walking a couple miles around campus. in my old high carb days I remember putting away liters before and after lunch and snacks too.
    I read somewhere that fat metabolism releases water molecules as a by product but havent followed up on how much that is significant. obviously food contains quite a bit of water too…

  16. Jill H 13 February 2010 at 12:30 am #

    As my grandmother would have said ‘I’m conflicted’. Not with the idea of maintaining hydration. I always remember a talk where the speaker explained the importance of making absolutely sure that elderly residence in care homes should have continuous access to drinking water and what a difference it had proved to be to their cognitive abilities and wellbeing if this simple procedure was carried out. My problem is with the whole industry of bottled water. I found it worrisome that on a visit to Bali a few years ago (which I had previously visited many years before and found of a breathtaking beauty), the island was drowning in plastic because presumably they do not have the mechanisms in place for recycling. I now live in California and work with marine mammals that are greatly injured by ingesting all of this plastic or getting entangled in other kinds of plastic that is finding its way into our oceans. I am also wondering these days why foods containing a high fluid content (a lot of fruits and vegetables ) could not be counted as having a hydrating affect, along with teas and coffees (in moderation of course) Why may not these foods and beverages be counted towards the quota of water thought to be beneficial and important to wellbeing? And if it does have to be pure water then hopefully there will be a movement towards more sustainable packaging of that water.

  17. Jamie 14 February 2010 at 1:31 am #

    This was a summary of some research being done at the University of Otago in New Zealand on this topic:

    [b]Hydration Hype Questioned[/b]

    Much is made of the need for correct hydration in sport and daily life, but Otago School of Physical Education researchers are adding to a growing body of research that questions the blanket guidelines.

    Dr Jim Cotter says much of the research into hypohydration (a state of lowered body fluid levels caused by the process of dehydration) is taken out of context, with findings based on exercise effects using unrealistic hypohydration levels created in artificially heat-stressful lab environments.

    Honours student Troy Merry found that athletes tolerate hypohydration better than untrained people when using realistic and controlled environmental and hypohydration conditions equivalent to about two percent of body mass.

    “The athletes showed none of the cardiovascular and thermoregulatory burden shown by untrained participants and promulgated in the literature.”

    The performance effects were unclear, but Cotter thinks the tendency for athletes to show slightly impaired performance may involve expectation or perceptions. “There was no apparent physiological reason for it. They may have regulated their performance according to perception – and thirst is a strong perception.”

    Cotter says common guidelines suggest that for every kilogram lost you should drink 150 percent of that to get it back. “In reality, much of the weight lost in prolonged competition or training is glycogen [stored sugars] and the water bound to it. There’s no point getting the weight back until you have resynthesised the glycogen – that can take a day.”

    He says aggressive rehydration is potentially more harmful than drinking according to thirst. “Surprisingly, it’s still unknown whether drinking to thirst will limit exercise performance.”

  18. Tina Rowen 15 February 2010 at 9:02 pm #

    Hello Dr.Briffa,
    my mom has high blood pressure and she is on drugs to dehidrate her. At the same time there are recommendations for her to drink more water for her overall health as blood results show that her blood is “thick”and this is quite conflicting. What is your advice regarding high BP and the amount of water intake? Thank you, Tina

  19. diane 7 October 2011 at 6:27 am #

    Hello Dr Briffa

    I’m trying to hydrate adequately & was interested in your article re urine colour as a measure. However as vitamin supplements change urine to a bright yellow colour, I’m told this is due to excess B2.. this doesn’t help me. Is there another suggestion you have for me & others in this position. I’m wondering is there a calculation based on weight? or something else.
    Many Thanks, Diane

Leave a Reply