Doctor's Note

This is one of those groundbreaking findings (like my gargling video) that will likely never see the light of day because there’s no profit motive for promotion. We’re guaranteed to be assailed about all the new drugs and surgical advances because there’s big business behind getting the word out. But who profits from tap water? Or even broccoli for that matter. That’s one of the reasons I created this site, to bring to light all the findings that would otherwise just get buried in medical library basements (or, increasingly, vast private databases). If you’ve found this site useful, please consider making a donation to keep this site alive and kicking.

The water content of plant foods may help explain why those eating plant-based diets are, on average, so slim. Like fiber, water is like a source of Nutrition Without Calories. See Dietary Guidelines: It’s All Greek to the USDA for a country with the guts to suggest water might be preferable to drinking soda. 

Juice and milk may not be as hydrating as water. What about tea? See my video Is Caffeinated Tea Dehydrating? What about Bottled Water vs. Tap? 

More on children’s health in videos such as:

Check out my associated blog post for more context:  Schoolchildren Should Drink More Water

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  • FruitandStrength

    “Imagine how much money drug companies could make if they told people to take a sugar pill with a glass of water”

    I wouldn’t give them no ideas, they’ll probably do it.

    • mark

      After an initial period of creating a drug & getting it approved, the cost to manufacture it soon drops to not much more than refining & tableting sugar.

    • erz

      I think maybe he was referring to vitamin supplements. To take a multivitamin in the morning, you would need a glass of water… so do you feel better from the multi or getting hydrated in the morning..

  • Benjamin Grunewald

    Good segment. I suspect much of the American public is walking around in a state of chronic dehydration due to drinking junk instead of water and not eating enough fresh fruit and vegetables. I would like to know what Dr. Greger thinks of the study of intracellular water volume done by the Murad Research Lab. I am somewhat of a Luddite and don’t know how to link to the study but it can be googled easily enough. In a nutshell, the study suggests that consumption of fresh fruits and vegetables is even more important than drinking large quantities of water in promoting high intracellular water volume. Is intracellular water volume a better measure of true hydration than urine concentration? I’m not sure but it sounds like it to me. Everyone should check it out.

    • Thea

      Benjamin: re: “…the study suggests that consumption of fresh fruits and vegetables is even more important than drinking large quantities of water…”

      I’m very interested in that too. I saw once saw an experiment on done on TV. It wasn’t an actual study. It was just a loose experiment. They took twins who were obsessed (my word) with drinking tons of water. The twins also ate fairly healthy – lots of fresh fruits and veggies. They had one twin skip the water (and all drinking) but eat the regular diet. The other twin continued with the massive drinking of water in addition to their regular diet. At the end of some short time (a week?) they tested both twins. I don’t remember exactly what they tested. It was probably not very accurate. But the idea was that both twins ended up with the same amount of dehydration.

      Ever since then, I’ve been fascinated with the idea that we might be able to get much or all of the hydration we need from something other than just water – as long as it is fresh food. I would love to know more about studies that follow up on this

      Thanks for sharing your information.

      • lyra

        I do hope that Dr. Gregor, or someone, can answer your question. Are fruits and vegies just as good, or perhaps better, for hydration as water? I’m also curious.

        • Benjamin Grunewald

          I feel inept for not knowing how to link to the study I wrote about but it is there if you just google “Murad water study”. The women who drank the most water had the lowest intracellular water volume!Sounds like good science but I am still hoping Dr. Gregor will weigh in on the quality and conclusions of the study.

  • Gerry

    We have been preaching the importance of water vs other beverages– many of which contribute to dehydration– so thank you so much for this excellent supporting evidence. May we also have the text of your spoken words above?
    Thanks in advance. –Gerry

    • b00mer

      Hi Gerry,

      Under the video there is a tab labelled “Transcript”. If you click on it you can get the full text of the video.

  • HereHere

    That’s pretty compelling research. Perhaps dry cereals, because of their dehydration, are doing no service to the children (beyond the harms of the sugar and possibly of the preservatives). It would be great to see similar research on adults. Do we go to work dehydrated most of the time? I’d like to know if your average soy milk has a similar osmolarity to the dairy milk cited in the research (300 mmol/kg I think it was – not 100% sure of the units)….oh, just found the research: it is 155-252 mmol/kg in Venezualan research. As someone who doesn’t like how the city water tastes, I’ll just have to spike it with some fresh lemon or lime and stick with that for my morning hydration.

  • Mike Quinoa

    How yellow or clear should your urine be to indicate you are adequately hydrated?

    • The yellow pigments in urine include urobilin, stercobilin (both bile acids from normal heme breakdown), but also the bright fluorescent vitamin riboflavin (B2), various carotenes (from carrots and also greens), red pigments from beets, blackberries or rhubarb, and eating enough fava beans can turn urine brown to black. See:

      So urine color isn’t just an indicator of hydration (where lighter might mean adequately hydrated), its also an indicator of the quality of diet (pigment nutrient dense fruits and veggies will color urine), supplementation, medication, as well as liver & kidney disorders.

      • Mike Quinoa

        Thanks for the response Darryl, and thanks for the osmolality chart. I can now see that urine color is a multi-factorial issue.

        • Just to add to Darryl’s excellent post all things being equal as far as dietary intake and medications clear urine is usually a sign of adequate hydration. I am a cyclist and it is important to maintain hydration especially on longer rides and on hotter humid days.

  • Thea

    I know that the beginning of the video talks about milk and juice as not being as hydrating as water. However, I would have liked to have seen more beverages tested. After watching videos on NutritionFacts, I’ve been under the impression (I’m just going off of memory here and may miss-remember) that drinking for example tea not only hydrates as well as water, but comes with extra nutrients. The conclusion is that tea is better than drinking water, because you get all of the liquid/water benefits plus the nutrients. Since tea does not have the sodium, sugars and amino acids listed in the video, I would expect tea to be fine.

    I would also like to know if almond milk has the same problem as cows milk in terms of helping or hindering hydration. Yes, there are amino acids, but presumably, the good ones. Hopefully they will do more studies on this and Dr. Greger can report to us.

    • There aren’t any comprehensive guides to beverage osmolality but here are some rough ranges (in mmol/kg):

      Red wine: 2500
      Beer: 1000
      Fruit juice: 500-700
      Sugary soft drinks: 415-500
      Cow’s milk: 270-390
      Sports drinks: 300-350
      Brewed coffee: 30-50
      Diet soft drinks: 30
      Tea: 30
      Tap water: 3

      Wesley, J. “Osmolality-A Novel and Sensitive Tool for Detection of Tampering of Beverages…” Microgram (2003): 8.
      Dini, E. et al. “Osmolality of frequently consumed beverages.” Investigacion clinica 45.4 (2004): 323.
      Mettler, S. et al. “Osmolality and pH of sport and other drinks available in Switzerland.” Schweiz Z Sportmed Sporttraumatol 54.3 (2006): 92,

      Fruit juice has higher osmolality than Coca-cola. Whoda thunk it?

      There was another study Grandjean, AC, et al. “The effect of caffeinated, non-caffeinated, caloric and non-caloric beverages on hydration.” Journal of the American College of Nutrition 19.5 (2000): 591-600.

      which found, contrary to received opinion, that “This preliminary study found no significant differences in the effect of various combinations of beverages on hydration status of healthy adult males. Advising people to disregard caffeinated beverages as part of the daily fluid intake is not substantiated by the results of this study.”

      Dr. Greger did a video on related paper which found caffeine in tea isn’t a diuretic:

      So I’m sticking to coffee at breakfast, green tea til dinner, hibiscus tea at night.

      • Thea

        Darryl: That is so nice of you to take the time to post this information.

        I don’t know what osmolality or mmol/kg are, but it is easy to get the gist of it from the context.

        That’s *fascinating* data. Thanks again.

        • Osmolality is simply the aggregate count of all the molecules dissolved in volume or weight of liquid, whether that liquid is a beverage or urine. 1 mmol is 6.02 x 10^20 molecules, and a kg of water is 1 liter. Each sugar, amino acid, or mineral atom has an equal “weight” in osmolality, so its really just a convenient but perhaps misleading measure.

          For water and other beverages, lower osmolality seems to lead to faster water absorption and less other stuff (carbs, minerals) added to body fluids, while for urine, high osmolality is a marker for dehydration.

          • Thea

            Thanks for the clarification. Much appreciated.

          • Nebuladance

            In simple terms, the amount of something dissolved in a liquid is an increase in its solutes. The way osmosis works is that when there is an area of higher solute concentration, water rushes in to balance the overall concentration (it is attracted by the electrical “charge” of the dissolved molecules). So a drink that contains a higher amount of solutes will cause water to be pulled FROM the tissues in order to balance it. A drink with low or no solutes will pull less or no water from the tissues. Instead, if the solute concentration in the tissues is higher than that of the drink, the water from the drink will rush to the tissues to balance them. Thus, hydrating the tissues rather than dehydrating them.

      • John Galt

        Regarding school children not drinking water: my kids have told me repeatedly they avoid going to the bathroom in public schools to avoid bathroom terror! In order to avoid having to go to the bathroom, they minimize water consumption and deliberately dehydrate themselves.

  • George Jacobs

    May we please have the references for one or more of the studies which suggested a link between water consumption by children and the children’s academic performance? Thanks.

    • Caroline

      Hi George, I wrote two of those papers. Here are the full references.

      Edmonds, C.J. & Jeffes, B. (2009). Does having a drink help you think? 6–7 year old children show improvements in cognitive performance from baseline to test after having a drink of water. Appetite, 53, 469-472.

      Edmonds, C.J. & Burford, D. (2009). Should children drink more water? The effects of drinking water on cognition in children. Appetite, 52, 776-779.

      best wishes, Caroline

      • Thank you so much for chiming in Caroline! George, links to all the sources are provided above if you click on Sources Cited.

  • Lovalife06


  • Great reminder of the importance of hydration and plain water. Thanks for another great one Dr. Greger. Even though I have an overactive bladder, I feel compelled to keep drinking.

  • BillG

    Did they ever say an optimal amount of water to drink in mild weather? I know I hear “8 glasses a day” but is this factual?

  • Coby Siegenthaler

    just did and it disappeared Coby

  • It cannot be overstated – drinking plain water and staying hydrated is key to good health for all ages! Very informative post and video – appreciate the sharing of this information.

  • stillwaters

    Loma Linda University researchers found that men who drank five or
    more 8-ounce glasses of water daily cut their stroke risk by 53 percent
    compared with guys who drank fewer than three glasses. Water helps to
    thin the blood, which in turn makes it less likely to form clots,
    explains Jackie Chan, Dr.P.H., the lead study author.

    But don’t chug your extra H2O all at once. “You need to drink water
    throughout the day to keep your blood thin, starting with a glass or
    two in the morning,” adds Dr. Chan.

  • Malcolm

    The only water we should all be drinking is hydrogen rich water.
    I have tons of scientific info on the therepeutic benifits of water that contains active hydrogen gas….the most powerful anti oxidant available.
    If anyone wants to cite that info send me an email via my website

    • Toxins
      • Darryl

        Its not alkaline water.

        There’s actually <a href="an interesting story on H2 enriched water, which has been studied primarily in Japan for the past decade. Molecular hydrogen is a nonpolar antioxidant that diffuses throughout the body (including hard to reach spots like mitochondria and brain), and selectively scavenges hydroxyl and peroxynitrite radicals. Turns out its remarkably cheap & easy to make:

        Hydrogen rich water was produced, by placing a metallic magnesium stick into drinking water (hydrogen concentration; 0.55–0.65 mM), by the following chemical reaction; Mg + 2H2O → Mg (OH)2 + H2. The consumption of hydrogen rich water for 8 weeks resulted in a 39% increase (p<0.05) in antioxidant enzyme superoxide dismutase (SOD) and a 43% decrease (p<0.05) in thiobarbituric acid reactive substances (TBARS) in urine

        I wouldn’t recommend leaving electrowinning pure magnesium ribbons in water bottles yet. The studies have largely been limited to animal models, there’s been not randomized controlled human trial to date, and I’d like to see more clarity on the adverse effects noted in the latter paper. But this may be a space to watch.

      • Darryl

        While Malcolm is marketing one of the $4000 alkaline water machines, there is active scientific interest in molecular hydrogen (H2) and H2 enriched water. This 2011 review surveys the research, while this paper details an inexpensive way of generating H2 enriched water, using magnesium. Do note the adverse effects experienced in the second paper.

  • Derrek

    Is drinking distilled water safe? I’m worried as I’ve been drinking it and that it has negative health effects.

  • Skeptic

    I once ate nothing but raw fruit and green leafy vegetables for several years, a so-called “fruitarian” diet. During several periods of over 30 days, it was unnecessary to drink any fluids at all because raw fruit and greens are about 80% water on average. I remained super hydrated the entire time.

    There’s some evidence that primates rarely drink fluids in nature for this reason. Anatomically too, we’re not particularly well adapted to drinking; imagine drinking without cups or other tools. Also low-fat diets tend to require less hydration because fats must be emulsified to be digested.

    In an ironic kind of way, it seems like I can somewhat judge the quality of my diet by how little supplemental hydration I need.

    • Thea

      Skeptic: Your post is quite thought-provoking.

      Not only do I appreciate it for its originality, but it backs up a non-scientific experiment I saw on TV some time ago. They took two identical twins who typically drink *a lot* of water in addition to eating lots of watery plant foods like tomatoes. They had one of the twins stop drinking any water/liquids for a week, but otherwise they both ate their normal diets. (Since they were living and cooking together at the time, they ate almost all the same things.) At the end of the week both twins had the same amount of hydration in their body. (However that was measured.)

      It’s really more of an anecdote, like your own story. But I think it is quite relevant. I have long been skeptical of the advice I have heard my whole life about how one has to drink X cups of water every day. I think the truth is not only much more of a “it depends”/”personal situation” on how much one must drink, but the advice is not as harmless as most people think. (I suspect.)

      Thanks for sharing.

      • Skeptic

        Its common in Fruitarian circles for people to not drink fluids. And you’re right, excess fluid consumption can be deadly, since it can, in a worse case scenario, overly dilute or wash out electrolytes. Its known as hyponatremia. So there are special situations where the advice to drink water is inappropriate.

  • Bruce Cropley

    Should we drink before, during, after and/or in between meals?

  • bobble

    as an adolescent I was a troubled kid and was in a residential facility. The therapist there would put kids on self harm precautions for not drinking enough water. a lot of people were on water logs. You would be surprised how hard it is to get eight cup of water every day. you don’t even feel thirsty a lot of the time. you have to drink about one cup every hour or two. and when you’re at work or at school the time goes by really fast. hydration is ridiculously important.