Image Credit: Sally Plank

How Much Water Should We Drink Every Day?

More than 2000 years ago Hippocrates (460–377 BCE) said, “If we could give every individual the right amount of nourishment and exercise, not too little and not too much, we would have found the safest way to health.” What does that mean when it comes to water? Water has been described as a neglected, unappreciated, and under-researched subject, and further complicating the issue, a lot of the papers extolling the need for proper hydration are funded by the bottled water industry.

It turns out the often quoted “drink at least eight glasses of water a day” dictum has little underpinning scientific evidence . Where did that idea come from? The recommendation was traced to a 1921 paper, in which the author measured his own pee and sweat and determined we lose about 3% of our body weight in water a day, or about 8 cups (see How Many Glasses of Water Should We Drink in a Day?). Consequently, for the longest time, water requirement guidelines for humanity were based on just one person.

There is evidence that not drinking enough may be associated with falls and fractures, heat stroke, heart disease, lung disorders, kidney disease, kidney stones, bladder and colon cancer, urinary tract infections, constipation, dry mouth, cavities, decreased immune function and cataract formation. The problem with many of these studies is that low water intake is associated with several unhealthy behaviors, such as low fruit and vegetable intake, more fast-food, less shopping at farmers markets. And who drinks lots of water? People who exercise a lot. No wonder they tend to have lower disease rates!

Only large and expensive randomized trials could settle these questions definitively. Given that water cannot be patented, such trials seem unlikely; who’s going to pay for them? We’re left with studies that find an association between disease and low water intake. But are people sick because they drink less, or are they drinking less because they’re sick? There have been a few large prospective studies in which fluid intake is measured before disease develops. For example, a Harvard study of 48,000 men found that the risk of bladder cancer decreased by 7% for every extra daily cup of fluid we drink. Therefore, a high intake of water—like 8 cups a day—may reduce the risk of bladder cancer by about 50%, potentially saving thousands of lives.

The accompanying editorial commented that strategies to prevent the most prevalent cancers in the West are remarkably straightforward in principle. To prevent lung cancer, quit smoking; to prevent breast cancer, maintain your ideal body weight and exercise; and to prevent skin cancer, stay out of the sun. Now comes this seemingly simple way to reduce the risk of bladder cancer: drink more fluids.

Probably the best evidence we have for a cut off of water intake comes from the Adventist Health Study, in which 20,000 men and women were studied. About one-half were vegetarian, so they were also getting extra water by eating more fruits and vegetables. Those drinking 5 or more glasses of water a day had about half the risk of dying from heart disease compared to those who drank 2 or fewer glasses a day. Like the Harvard study, this protection was found after controlling for other factors such as diet and exercise. These data suggest that it was the water itself that was decreasing risk, perhaps by lowering blood viscosity (blood thickness).

Based on all the best evidence to date, authorities from Europe, the U.S. Institute of Medicine, and the World Health Organization recommend between 2.0 and 2.7 liters (8 to 11 cups) of water a day for women, and 2.5 to 3.7 liters (10 to 15 cups) a day for men. This includes water from all sources, not just beverages. We get about a liter from food and the water our body makes. So this translates into a recommendation for women to drink 4 to 7 cups of water a day and men 6 to 11 cups, assuming only moderate physical activity at moderate ambient temperatures.

We can also get water from all the other drinks we consume, including caffeinated drinks, with the exception of stronger alcoholic drinks like wines and spirits. Beer can leave you with more water than you started with, but wine actively dehydrates you. However, in the cancer and heart disease studies I mentioned above, the benefits were only found with increased water consumption, not other beverages.  

I’ve previously touched on the cognitive benefits of proper hydration here: Does a Drink Of Water Make Children Smarter?

Surprised tea is hydrating? See my video Is Caffeinated Tea Dehydrating?

Surprised that the 8-a-day rested on such flimsy evidence? Unfortunately, so much of what we do in medicine has shaky underpinnings. That’s the impetus behind the idea of evidence-based medicine (what a concept!). Ironically, this new movement may itself undermine some of the most effective treatments. See Evidence-Based Medicine or Evidence-Biased?

How else can we reduce our risk of bladder cancer? See Raw Broccoli and Bladder Cancer Survival.

What kind of water? I recommend tap water, which tends to be preferable from a chemical and microbial contamination standpoint. What about buying one of those fancy alkalizing machines? See Alkaline Water: a Scam?

It’s so nice to have data on such a fundamental question. We have much to thank the Adventists for. You will see their studies cropping up frequently. See, for example, Plant-Based Diets and Diabetes, The Okinawa Diet: Living to 100, and Evidence-Based Eating.

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Discuss

Michael Greger M.D., FACLM

Michael Greger, M.D. FACLM, is a physician, New York Times bestselling author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous "meat defamation" trial.


68 responses to “How Much Water Should We Drink Every Day?

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  1. Dr. Greger, how amount carbonated mineral water? It’s actually a two-part question….
    are the minerals absorbable/usable by the human body (i assume minerals in mineral
    water are “rocks”, in a way. And, how about the carbonation that is added? Is carbonation
    in water (when it is added to product) harmful in any way to gut? Green light on this one?
    I sometimes like to buy the german carbonated mineral waters and they have very very
    hight total dissolved solids counts, well over 2,000. The most popular one here in Germany
    is 2,500 total dissolved solids (lots of magnesium and calcium). But hey, maybe this water
    is a waste, as far as mineral usability in human body. And just maybe the added carbonation
    is harmful in some way. Most people here think this stuff is harmless, as they do in the States
    as well. Thanks for comments.




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    1. Thanks for your question Greg.

      I found one review that states:

      “In one trial, researchers compared the utility of carbonated mineral water in reducing functional dyspepsia and constipation scores to tap water in individuals with functional dyspepsia.75 When comparing carbonated mineral water to tap water, participants reported improvements in subjective gastric symptoms, but there were no significant improvements in gastric or intestinal function. The authors indicate that it is not possible to determine to what degree the mineral content of the two waters contributed to perceived symptom relief, as the mineral water contained greater levels of magnesium and calcium than the tap water.”

      Another study reports potential benefits of carbonated water on swallowing ability:

      “It was suggested that carbonated beverages are easy to swallow and effective for improving pharyngeal swallowing.”

      There is not much research on carbonated water, and I could not find a review that analysis the effect of carbonated water on health in general but I hope this answer helps.




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    2. Since carbonated mineral water is the beverage of choice for a majority of people in Germany (I am German and grew up there so can judge), I would assume it’s quite safe, or else we would know by know :-) Also, as you may know, regulations for food safety (and pharmaceuticals, too, of course – you’d never find Aspirin in the grocery store, these things are strictly NOT over-the-counter in Germany. As they shouldn’t be, in my opinion!!) are very strict, so if these minerals were at all dangerous, I’m sure they wouldn’t have been on the market for decades. Drink away, I’d say – definitely a lot healthier than all those horrible sodas there are in the States!!!




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    3. Dr. Greger, how could you in good conscience recommend that we drink tap water? Just a week or two ago you were talking about the lead in tap water. There’s so much more to be concerned with here. I could never counsel my clients to drink unfiltered tap water knowing from first hand experience what municipal water systems put in the water.




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  2. Years ago I read “Your Body’s many cries for water” by Batmanghalidj (?), an Iranian doctor. Has anyone else read that? He felt his research would never be well known because there’s no profit in drinking water.




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    1. Dr. Batmanghalidj has additional books beyond the book “Your Body’s many cries for water”. In addition, he has a peer reviewed article “Neurotransmitter Histamine: An alternative view point” in the 3rd Interscience World Conference on Inflammation, Antirheumatics, Analgesics, Immunomodulators. Monte-Carlo (Principality of Monaco), March 15-18, 1989, In WIN 89. In brief, his research states that all functions of the body need water because the body is primarily composed of water. Disease in the body is primarily the result of dehydration and a lack of minerals and salt in the body. By proper water hydration and minerals, disease states can be reversed as long as the dehydration has not progressed too far. He gives examples of individuals who reversed their conditions through proper hydration. Recommend reading his materials including “Your Body’s many cries for water”.




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    2. hi Joy Tuman, I downloaded an 11 page pdf file “Your body’s many cries for water” by the author you mention. I have not read it yet, though it looks really interesting. I just have one question re his recommendation for 1/4 tsp salt per quart of water. At NutritionFacts there are a number of videos and articles recommending low/no salt added to the diet (other than naturally occuring sodium in vegies) Do you add salt to your drinking water ?




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      1. Just a thought and nothing truly scientific, but I often wonder if the issue with table salt isn’t just the sodium, but the processing, since it alters the natural balance of components, and we all know WHOLE foods of any kind trump the altered approximations. I also will not pay $6 a lb for Himalayan pink salt or whatever the current market darling is, but considering the polluted ocean (including decades of nuclear waste) is the source of most processed salt, the double whammy of processing and concentrating it just does not seem too healthy to ingest. Most of us probably don’t need much additional sodium, but here in South Florida, the runners, bikers, and other athletes would drop like flies from electrolyte issues trying to stay hydrated without it, so I would love to know the science.




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        1. Try reading Dr. David Brownstein’s “Salt Your Way to Health”. You might be able to find some UTube or other videos online for his presentation material. Although, he seems to promote a certain brand of salt he used his many patients where he has obtained his observations and used his protocol to back up his findings. An interesting book.




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          1. Hi Sophie,

            The peer reviewed science tells us that the ingestion of salt is bad for us. Unless Dr Brownstein can provide peer reviewed science on the benefits of his approach then I would consider it dangerous to promote him.




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  3. “Your Body’s many cries for water” is a great study of water. I have also read it many many times as IO attempt to follow it. Works for me.




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    1. I’ve read all his books, too. Many are repetitive of material published in other books of his. They are highly informative and impressive. He was a doctor, not a writer, per se, so they need better organisation. The cancer cures are something else.




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  4. I am 65. At age thirty while playing basketball, I fell on my tailbone and herniated two discs, the L-4/L-5 and L5-S1. For the next thirty years, I suffered from terrible bouts with “lumbago” and low back pain that often left me unable to sit comfortably and in some cases nearly immobile for days at a time. I managed it with chiropractors and lumbar manipulations (a good thing), and anti-inflammatories (probably a bad thing for the lining of my stomach in the amounts I needed to relieve the pain.)

    Then, about five or six years ago, I was visiting a friend in DC and had a bout. He got me into his chiropractor, the amazing Dr. Philip Bahnson. I walked into his treatment room and lay down on my back so that he could do the customary “figure 4” with one leg up and the doctor applying his body weight to get the necessary “pop” that would alleviate inflammation and get blood flowing to the site again. Dr. Bahnson asked that I first lay on my stomach.

    I did so, and he put his finger on the epicenter of my pain directly and immediately, without even lifting my shirt or looking at anything. I flinched.

    “That’s on your kidney meridian,” he said. “How much water do you drink a day?”

    “I drink mostly coffee,” I replied.

    “So try drinking three or four good glasses of water a day–and maybe cut back on the coffee, since it dehydrates.”

    I followed his instructions and my bouts with lower back pain have nearly disappeared. I have had to go to a chiropractor maybe three or four times in the past five or six years. (Previously I was going a dozen times a year. In fact, I chose my health coverage plan according to best chiropractic coverage.) So thirty years of pain might have been alleviated had I run into Dr. Bahnson then rather than more recently.

    I have read a number of naysayers about water consumption on sites elsewhere, so I wanted to post my experience. I realize that it is “only” anecdotal and therefore would not fit into Dr. Greger’s cited studies (I have dogeared MANY pages in How Not to Die), but if my story can help just one person avoid the pain I had for so long …




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  5. I still find it surprising that you recommend tap water, even after your recent article about lead contamination in drinking water. What are your thoughts on tap water’s contamination of chlorine, fluoride, heavy metals, trace plastics and pharmaceuticals?

    What about Reverse Osmosis filters? I know they strip the water of trace minerals, but if you add the minerals back in afterwards, isn’t this better than tap water??




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    1. I like my Berkey water filter. It takes out the bad stuff – chlorine and fluoride, etc., but leaves the nutritional minerals. We bought it to take on a 6-week car trip, and it was rather large and awkward to take into our hotel rooms at night, but we were so glad to have it. We’ve used it ever since.




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  6. Thank you so much for this article and all that you do, Dr. Greger!!

    Could you please tell us… Are there any pros or cons about drinking distilled water?

    Thank you!
    Mark




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    1. I did a little research on this issue and found what appears to be most comprehensive study was done for the World Health Organization; http://www.who.int/water_sanitation_health/dwq/nutrientschap12.pdf
      HEALTH RISKS FROM DRINKING DEMINERALISED WATER Frantisek Kozisek National Institute of Public Health Czech Republic It summarized:: “Demineralised water that has not been remineralized, or low-mineral content water – in the light of the absence or substantial lack of essential minerals in it – is not considered ideal drinking water, and therefore, its regular consumption may not be providing adequate levels of some beneficial nutrients.” Perhaps that’s why Dr Greger commented : ” What kind of water? I recommend tap water, which tends to be preferable from a chemical and microbial contamination standpoint…” Hope this helps…




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      1. Hope I’m not coming across as argumentative, but I’ve been drinking distilled water exclusively for about the last ten years. AFAIK, I’m in good health.

        But I don’t drink a lot of just plain water… in the summer probably half is that way while the other half and almost all of my winter intake is with brewed tea.

        My water is distilled from RO water in a stainless steel distiller and as it leaves the spout, it never touches anything other than glass.




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        1. Same here, Lonie. I’ve been doing exactly the same thing for about 5 years. No problems.

          Was just wondering if there was any solid science on it. I guess the ‘Distilled Water Board’ hasn’t been funding any studies. ;-)




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          1. Heh! Probably not a Distillers’ Water Board study. ‘-)

            And maybe the advice to only drink mineralized water is good advice… if you subsist off a low-nutrient starchy fare in some poor area.

            But I think in most areas of the globe a person who can afford to drink distilled water is also able to afford a range of foods that contain all the minerals a body needs… and such a person who is smart enough to choose distilled water is smart enough to choose nutritious foods.

            My only mild concern is that distilled water acts as a solvent due to its neutral pH. That’s one reason I only keep or drink it from glass.

            That is, it could leach out components from metal (even stainless steel over time) and especially from plastic. In the past I’ve put a few drops of liquid minerals in my water in case it was a concern for my body leaching out minerals from using distilled water. I eventually discounted that happening because when water hits our stomach it is mixed with stomach acid.

            If that doesn’t change the properties of the water (pH) then I don’t know what will.

            I do currently add a drop or two of food grade Hydrogen Peroxide (cut to approximately 10% strength from original 17%) per gallon of water. No scientific basis for this… just a gut feeling.




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          2. Forgot to mention… AFAIK, distilling water is perhaps the only method of water preparation that kills both gram Positive and gram Negative organisms.




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  7. I was a little surprised to read that Dr. Greger says that he recommends tap water (“which tends to be preferable from a chemical and microbial contamination standpoint”) as his preferred source of water. I wondered if this was a misprint. Dr. Greger recently had a video about lead in drinking water.

    Some city water quality reports are available from the EPA website.
    https://ofmpub.epa.gov/apex/safewater/f?p=ccr_wyl:102

    For a long time I drank distilled water with trace minerals added. I recently switched over to a Gold Seal Certified 5-Stage Reverse Osmosis Drinking Water Filter System that cost less than $200. It states that it filters 1,000+ water pollutants including chlorine and fluoride. The thin-film composite semipermeable RO membrane filters down to 0.0001 micron (a human hair is approximately 50 microns).




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      1. Check out Big Berkeys. They leave the minerals intact. I became mineral deficient using a reverse osmosis system. They actually leach minerals out of your body. We have had both a distiller and a state of the art reverse osmosis system. They are both in the garbage. I didn’t sell the RO system because I felt it would be like selling a car with no brakes to someone without telling them. Plus RO systems waste water.




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        1. If you are eating all the greens, nuts and fruits you should you will not be deficient in minerals. I drink a gallon of distilled (The only way to make water really pure) and eat a balanced, whole food Vegan diet and I have no problem. This leaching of minerals is a myth!




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  8. Interesting that you recommend tap water to drink. Tap water typically is treated with fluoride with the “advertisement” that it prevents cavities/caries in children’s teeth. Yet fluoride is a poison and many say there is no evidence that it prevents cavities. Studies I have found indicate that it causes cavities and some say it is a carcinogen. If we are going to stick to science based evidence then please substantiate with evidence why fluoridated tap water is healthy for us.




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  9. My observations suggest that the essential minimum volume of water needed to stay hydrated is closely associated with the nature of the foods being eaten :

    Group 1 – eating most highly processed and calorically dense foods (examples : meat, dairy, crackers) – will need highest fluid intake to maintain hydration status, and not to overlook the moisture that needs to be added for successful digestion and elimination. As someone once said to me in regard to very low moisture foods like hard crackers – “You’d better hope they aren’t coming out the way they went in!” (in other words – water needs to come from somewhere).

    Group 2 – whole foods plant based diet – foods, especially uncooked, with the highest moisture content, and lower caloric density. Much more ‘digestion ready’ – less need for added fluids.

    Group 3 – raw vegan – members of this group do not eat from cooked food sources, if implementing at 100%. Fresh fruits, leafy greens, very limited quantities of nuts. I have seen committed raw vegans/Natural Hygienists getting by with drinking NO water. If thirsty, they tend to eat from amongst juicy fruits. Hard to believe? It is true.

    One added note : I suspect, but can’t prove, that water is actually assimilated a lot less efficiently by drinking as a straight liquid, than it is when taken in associated with the structure and chemistry of ideal nourishing food sources – think of the juiciest of fruits here.

    Those of us with a moderate level of experience of water-based therapeutic fasting have insights into this syndrome. (fasters are slightly dehydrated during the course of the fast, even though they are doing precious little except drinking liters of water and resting).

    Grant.




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    1. Great breakdown Grant! To suggest a raw vegan would need to drink the same amount of water as a meat eater is preposterous, there is no water in the standard American diet – which uses water in order to digest rather than providing it. In other words, some diets actually need water just to help move stool through the body while others would not at all (remember we aren’t supposed to drink when we eat right, why?). Until someone studies water’s effect using the breakdown you provided, I don’t want to know what helps those with dietary issues (which is what the SAD diet is, a sickness). I also really appreciate Steve B’s comment on using pee colour to determine where we’re at specifically… I’d suggest monitoring your mouth as well (is it dry? drink something!), simple right?

      Eating plants ensures water, we likely evolved to take water from food specifically if you think about it, how amazing plants convert the sun into energy and even store the water they used to grow from deep in the ground, which releases when we juice it in our mouths, brilliant! I also think there actually is a such thing as drinking too much water but if we solely rely on the evidence of studies that never seem to do a great job even identifying the basic factors that should be tested is it really scientific?

      And tap water??? EW, sorry but I will use a filter and love that a previous commentator on this thread even brought their Berkey on a road trip, AWESOME!! Tap water in Canada is mostly recycled, meaning it came from our toilets. More disgusting, out of the five stages of public water filtration we could apply, we only do three stages of filtration, which leaves a chlorinated slurry for us to drink, yum! Not all of our cities have removed fluorine as well so to make a blanket recommendation as if we all have the same “clean” tap water is rather naive (and dangerous) if you ask me. Pass the Berkey please :)




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  10. One of the gaps in most articles on water and hydration (including today’s blog) is no attention paid to too much water. Hyponatremia is pretty rare, but short of that, can you get too much water? I can’t cite studies but my understanding is that consuming significantly more water than we need forces the body to dump excess water and the mechanism for doing that is to dump electrolytes (water follows salt), which is not a desirable thing to do chronically or during endurance exercise (over one hour). The simple way to assess one’s hydration (rather than an impossible algorithm including size, level of activity, ambient temperature, portions of fruit and vegetables, and amount of fluids consumed) is to monitor urine color. Dark yellow means dehydration. Clear or near clear indicates over-hydration. Straw (or champagne) color indicates your in the healthy range of hydration.




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    1. Some wacko DJ locally had a contest to see who could drink the most water the fastest. A young woman died from doing it. I don’t remember how much she drank, but it was a lot in a short period, like maybe a gallon in an hour. She lost her minerals and died!




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    2. I do not believe the colour of your urine is a valid way to measure hydration. The colour does vary with volumes of water but it also varies with what you eat. I eat mainly a whole plant diet and my urine is always dark coloured. There is a danger is drinking too little and also too much. When I am thirsty I drink but not otherwise. The first aid for dehydration is to give a half cup of water and wait 5 minutes. Then offer another half cup. Giving a thirsty person a lot to drink can tip them over into Hyponatremia.

      https://www.scientificamerican.com/article/strange-but-true-drinking-too-much-water-can-kill/




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  11. We use filtered water from the refrigerator for cooking and drinking. Let me know any recommendations on good whole house filtration systems.




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  12. I recommend Colin Ingram’s book “The Drinking Water Book” (second edition) for a very thorough treatment of water quality and filtration options. Though a little dated, it is an excellent and readable book on the subject of water purification, including what national standards labels to look for in water purification systems.




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  13. He recommends tap water, with chlorine, THM’s, agricultural chemicals, and who knows what else? How about filtering it?




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  14. Hi Michael et al

    Thanks for helping me look at the science through new eyes.

    Would love someone to help me understand how it is a study can tease apart the confounding factors and then confidently proclaim … “after controlling for other factors such as diet and exercise.”




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  15. I drink a lot of coffee. Fortunately or unfortunately, I and related females, suffer from low blood pressure and postural hypotension. I spend a lot of time waiting to be able to see when I stand up. Not a big deal except for occasionally it’s more severe leading to temp loss of consciousness which can lead to injury. Coffee seems to help. And I drink quite a lot of water as well. My doctor speculates it’s a form of self medication. There’s no evidence so I’ll leave it at, it seems to help. I’m glad this counts as hydration. Otherwise I’m one of the lucky few blessed with stalwart health, perhaps aided and abetted by a whole food plant based diet. Nothing fancy or extreme. Lots of whole grains and delicious pulses, greens, and fruit. I like to eat. Food is and should always be a source of joy.




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    1. basically, take your weight in kg times 0,03 results is in litres… so if you weight 100 kg you should drink 3 litres per day, wish you all the best

      Betty




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  16. Regarding the color of our urine…

    I do like the idea of drinking enough to generally have lighter color urine, but I ate some beets once and later on for a moment I thought I had internal bleeding. ;)

    Cheers!
    Mark




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    1. Yes Mark, I experienced the same moment of shock after making a beetroot based smoothie. Another aspect of drinking too much water is the need to pee all the time. This can interrupt a good night’s sleep and add to fatigue. If we are drinking all day and peeing all night then when do our kidneys have a chance to recover?




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    1. Kelly, the rule of thumb I learned is to drink half as many ounces as your weight in pounds. So you weigh 92, half of that is 46, so that would be 46 ounces. I don’t know if that is a valid rule or not, but I learned it in a nutrition class.




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      1. Kelley, Yes, that is the generic formula, before all the variables (size, level of activity, ambient temperature and humidity, etc.) are taken into account.




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    2. Hi Kelly,

      From what I have read about Turner’s Syndrome this is not relevant to the quantity of water you should be drinking. I suggest you put this question to your doctor. My own philosophy is to drink whenever I am thirsty. I think the best answer to how much a person should drink every depends on who they are, what they do, where they live and what else they consume.
      There are too many factors to take into account so let your own thirst be your guide. One more thing I would like to say is make sure you stop drinking long enough before bedtime so you are not getting up all night to go to the toilet. Otherwise your REM sleep will be disrupted and you will feel it the next day. These links might interest you.

      http://www.scientificamerican.com/article/strange-but-true-drinking-too-much-water-can-kill/

      http://drbenkim.com/drink-too-much-water-dangerous.html




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        1. Like you, my only water intake is from distilled water… that is, I cold brew tea in distilled water that goes right into glass as it is distilled and continues into glass until consumed. I distill about 140 gallon jugs of water (I’ve drunk a lohhhhht of organic apple juice over time to get that many empty glass jugs ‘-) during the winter months in order to heat a room in the house where I spend a lot of time.

          I keep a 6 jug rotation of Carlo Rossi 4 liter or whatever, wine bottles encircled with magnetic tape and small magnets on the tape to boost the magnetism (science finally acknowledged, some years ago, that you can change the properties of distilled water through electrolysis). Before entering a bottle of the water into service I add two drops of food grade H2O2 (Hydrogen Peroxide) that has been reduced to less than 10% pure.

          And while I know HP is an oxidant, I take and consume enough anti-oxidants to handle the amount added. And I believe, but have no proof, that the distilled water + the HP helps to brew my different teas quicker and stronger.




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  17. I’m not so sure that drinking large amounts of tap water is such a good idea. Most municipalities add fluoride to the water supply. There is also the chlorine that is used as well. The chlorine is used primarily to kill viruses and bacteria. Boiling water might drive off any residual chlorine, but boiling will not remove fluoride. They say the fluoride is added to improve dental health, but I haven’t seen any studies that prove this. Fluoride is a poisonous element and has been linked to cancer and reduced IQ. So, drinking seven or eight cups of tap water a day may not be such a good idea. What do scientific studies say?




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  18. I put this information
    together to help a friend of mine in her eighties, who despite having
    experienced amazing benefits from “the water cure” (including normalized eye
    pressure and blood pressure, after years of glaucoma and severe
    hypertension) continually received negative feedback from friends and
    doctors about the dangers of her drinking 6-8 cups of water a day. So I put
    together some factual medical and research information to help her respond
    when confronted by two myths:

    1. Many people incorrectly assume that if you drink a liter or two of
    “extra” water” so that you urinate twice as much, this will put a strain on
    your kidneys because they have to work twice as hard. In fact, the
    additional work amounts to an extra 1-2 %, if that. (Kidneys do most of
    their work in filtering fluid and solutes and then reabsorbing them – not in
    passing them on.) On the other hand, dehydration does force the kidneys to
    work harder in order to eliminate toxins, balance metabolites, and to create
    urine in a concentrated state.

    2. Many people, even doctors, incorrectly assume that no matter what your
    age, you should only drink when you feel thirsty. Most older individuals
    experience hypodipsia – a reduced ability to feel thirst. The bodies of
    older people can become dehydrated – even pathologically dehydrated –
    without their feeling thirsty at all.

    Some research studies:
    Changes in total body water with age.
    Am J Clin Nutr. 1989 Nov;50(5 Suppl):1176-81
    Schoeller DA.
    Department of Medicine, University of Chicago, IL.
    Extensive cross-sectional studies demonstrate a diminution of total body water in elderly and very old subjects. These findings are supported by less extensive longitudinal studies. Cross-sectional studies indicate that the decrease in total body water is mainly due to decreased intracellular water, but this is not supported by the findings of longitudinal studies. Despite the observed changes in total body water, both animal and human studies indicate little or no change in the relationship between total body water and fat-free mass with aging.
    PMID: 2683726 [PubMed – indexed for MEDLINE]
    Effects of hypertonicity on water intake in the elderly: an age-related failure.
    Geriatr Nephrol Urol. 1997;7(1):11-6.
    McAloon Dyke M, Davis KM, Clark BA, Fish LC, Elahi D, Minaker KL.
    Division on Aging, Harvard Medical School, Charles A. Dana Research Institute, Beth Israel Hospital, Boston, MA 02215, USA.
    Dehydration is a common clinical syndrome associated with many illnesses and treatments in the elderly. Prior studies have shown diminished sensation of thirst during water deprivation. It is currently unclear whether age-related decreases in thirst perception impair the defense against a hyperosmolar challenge. To examine the impact of water ingestion during hyperosmolality, young and old subjects were allowed free access to water during and after an intravenous infusion of 5% hypertonic saline. Cumulative water intake and serum osmolality were compared between seven healthy young (20-28 yrs) and seven healthy old (72-89 yrs) volunteers during and following a two hour hypertonic saline infusion at a rate of 0.06 mlxkg(-1) min(-1). Serum osmolality and water intake were markedly different between the two groups. In the old group, serum osmolality increased by 17 mosmol/kg above baseline despite free access to water. In contrast, serum osmolality increased to only 7 mosmol/kg above baseline in the young group and did not rise further. By ingesting water, the young were able to defend against an additional increase in serum osmolality. The young drank approximately twice that of the old during the infusion period. Healthy older individuals drink less than young despite a significantly increased serum osmolality. This hypodipsia in old individuals increases their susceptibility to hypertonicity.
    PMID: 9422434 [PubMed – indexed for MEDLINE]
    Effect of hydration state on strength, power, and resistance exercise performance.
    Med Sci Sports Exerc. 2007 Oct;39(10):1817-24.
    Judelson DA, Maresh CM, Farrell MJ, Yamamoto LM, Armstrong LE, Kraemer WJ, Volek JS, Spiering BA, Casa DJ, Anderson JM.
    Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, CT, USA. djudelson@fullerton.edu
    PURPOSE: Although many studies have attempted to examine the effect of hypohydration on strength, power, and high-intensity endurance, few have successfully isolated changes in total body water from other variables that alter performance (e.g., increased core temperature), and none have documented the influence of hypohydration on an isotonic, multiset, multirepetition exercise bout typical of resistance exercise training. Further, no investigations document the effect of hypohydration on the ability of the central nervous system to stimulate the musculature, despite numerous scientists suggesting this possibility. The purposes of this study were to examine the isolated effect of hydration state on 1) strength, power, and the performance of acute resistance exercise, and 2) central activation ratio (CAR). METHODS: Seven healthy resistance-trained males (age = 23 +/- 4 yr, body mass = 87.8 +/- 6.8 kg, body fat = 11.5 +/- 5.2%) completed three resistance exercise bouts in different hydration states: euhydrated (EU), hypohydrated by approximately 2.5% body mass (HY25), and hypohydrated by approximately 5.0% body mass (HY50). Investigators manipulated hydration status via exercise-heat stress and controlled fluid intake 1 d preceding testing. RESULTS: Body mass decreased 2.4 +/- 0.4 and 4.8 +/- 0.4% during HY25 and HY50, respectively. No significant differences existed among trials in vertical jump height, peak lower-body power (assessed via jump squat), or peak lower-body force (assessed via isometric back squat). CAR tended to decrease as hypohydration increased (EU = 95.6 +/- 4.9%, HY25 = 94.0 +/- 3.1%, HY50 = 92.5 +/- 5.1%; P = 0.075, eta(p)(2) = 0.41). When evaluated as a function of the percentage of total work completed during a six-set back squat protocol, hypohydration significantly decreased resistance exercise performance during sets 2-3 and 2-5 for HY25 and HY50, respectively. CONCLUSION: These data indicate that hypohydration attenuates resistance exercise performance; the role of central drive as the causative mechanism driving these responses merits further research.
    PMID: 17909410 [PubMed – indexed for MEDLINE]




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  19. You recommend tap water? Haven’t you seen recent studies that show, on top of dangerous fluoride, tap water contains all manner of pathogens and high levels of drugs, including antibiotics and hormones? I can’t believe you recommend tap to your readers.




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    1. I agree with Claudia – our tapwater is DISGUSTING!! We have a whole house water filtration system and still prefer to drink the water from the fridge filter – that’s basically double-filtered and tastes fine. But I’m sure that doesn’t contain a lot of minerals etc. anymore!




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  20. A couple of questions if anyone can help:

    It makes sense that a darker urine may indicate dehydration, but don’t certain fruit and vegetables “dye” your urine a darker colour?

    Since a whole foods, plant-based diet naturally entails a lot of carbohydrates, isn’t water created in the digestion of those carbs? Could this make the volume of your daily urinary excretion somehow greater than your fluid intake?




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    1. The only items I am aware of that alter the color of urine are beets (red) and Vitamin B supplements (yellow). I support using urine color as a guide for assessing hydration, recognizing these factors. For B vitamins, best to get them from food. For beets, just be aware when you eat beets. So knowing these things, one can take them into account when assessing hydration via urine color.

      And yes, the body both uses water (e.g., in the digestion process in which hydrolysis uses water as it splits the components of starch,fat and protein), and produces water when sugars, amino acids and fatty acids are “burned” resulting in water and CO2 and via dehydration synthesis (when the body reconstructs it’s own proteins, triglycerides and carbohydrates such as glycogen. I’m not sure what the balance is between using and producing water, and I’m not sure how useful knowing this is. My advice is to monitor urine color.




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  21. Am very glad to see so many comments about Dr. Batmanghelidj’s book(s). I have his “You’re Not Sick, You’re Thirsty” and try hard to abide by the ‘half your weight, in ounces’ of water daily. So if you (male or female) weigh 150 pounds, that’s 75 ounces of water. I personally prefer spring water if at all possible. Maybe it’s possible to”OD” on too much water, but I can’t imagine it; certainly I think drinking “excess” water is preferable to the USDA’s stupid recommendations of ‘just get your fluids from any place’. With the pro-business pro-Trump regulators now in place, that’ll be milk, beer, vodka, coffee, tea any where you want: certainly NOT from vegetables or fruits. FYI, am also a fan of “How Not to Die” & hope to keep myself healthy as I turn 70 in September. Thanks for letting me have my say and for this great website.




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    1. Yes, you can kill yourself by drinking too much water, too fast.

      “”Rapid and severe hyponatremia causes entry of water into brain cells leading to brain swelling, which manifests as seizures, coma, respiratory arrest, brain stem herniation, and death,” M. Amin Arnaout, chief of nephrology at Massachusetts General Hospital and Harvard Medical School told *Scientific American*.”
      http://www.medicaldaily.com/water-intoxication-just-how-much-h2o-does-it-take-kill-person-312958




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  22. I was very curious about this subject years ago, and I found two sources referencing 8 cups of water a day, going back much earlier. John Harvey Kellogg appears to have been recommending this at his health sanatorium by the turn of the 20th century; I was never able to pin down his source, though he was very interested in studies about water in the body of the time. I also read a book from 1908: A System of Diet and Dietetics edited by GA Sutherland, published by Oxford Medical Publications. In it is a scientific study reference: “Atwater and Benedict found that, upon an ordinary diet, an individual not doing muscular work took on an average about 4 pints of water a day in a 49 days’ experiment; this includes that taken in the solid food as well as in liquids.” While I could not find the actual article, Atwater and Benedict are well-documented as doing a lot of ground-breaking, precise work about respiration and metabolism, based on a variety of people. The article by EF Adolph linked in the article above also references earlier studies on water drinking as well; so it was a topic of interest, though the Atwater and Benedict was the earliest precise reference to specific studies that I could find. Key point in the Atwater and Benedict stuff that I read: the exact amount lost by the body depended on exertion, ambient temperature, diet, and body size. So we need water, but the there’s not an easy answer to a minimum amount or an optimal amount. The ranges suggested in the article seem reasonable.

    @Mike Quinoa
    1) there are a lot of factors to urine colour; for example, see https://health.ucsd.edu/news/features/Pages/2014-04-21-colors-that-suggest-urine-trouble.aspx However, if I have taken a vitamin B supplement, I’ll have deep yellow urine, another factor they don’t mention there, but which can be found elsewhere. So yes, food affects colour, too.

    2) Yes, carb metabolism creates some water; the article above acknowledges that. Because we constantly excrete water through our skin, lungs, faeces, etc. as well, your total urinary output will never be as high as your total fluid intake under normal circumstances. I think because of this it would be hard to calculate the exact impact on urinary output; it could also be affected by other related dietary changes. For example, decreased concentrated protein consumption is also associated with a lower dietary water need (sorry, I don’t have that journal reference nearby)–whether that is from metabolic need, or the increase of water from carb metabolism, is an example of why your question seems rather complex to address.




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  23. I know nutrition, age, weight and height play into how much water I should consume. I was wondering about how much I should drink.




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        1. In a nutrition class I took some years ago they recommended we drink 1/2 ounce for every pound of body weight. So, if you weigh 150 pounds, drink 75 ounces of water. Drink extra if you indulge in coffee, soft drinks or alcoholic beverages, which are dehydrating. We were also told that tea is dehydrating, but Dr Greger has a video showing research that shows otherwise.




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  24. My Nephrologist recommended to me take as little as 1 qt up to 1 1/2 qts. My blood sodium and chloride had been low for several months. I am now normal after 1 month and feeling better.




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