Hydration 101: How Much Water Do You Really Need? | Chris Kresser

Hydration 101: How Much Water Do You Really Need?

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Eight ounce glasses of water, eight times per day: this has been the water drinking mantra pushed by health professionals, beverage companies, and popular media for decades. From the number of people sipping on water bottles on a constant basis, it seems like the “drink more water” message is getting through. But is this message accurate? And where did it come from?

It may surprise you to learn that there has never been any scientific evidence to support the “eight by eight” doctrine when it comes to proper hydration. The first recorded scientific endorsement of a water intake recommendation appeared as a brief footnote in 1945, when the Food and Nutrition Board of the National Academy of Sciences published its Dietary Guidelines. (1) And like many other nutrition recommendations, it appears that individual needs for water vary widely, and 64 ounces of pure water every day may actually be too much for some people. (2) So how do you determine how much water you need as an individual?

There is no evidence to support the recommendation to drink 8 glasses of water a day.Tweet This

How much water do you really need?

There’s no question that adequate hydration is important, as water is a critical nutrient, but the eight by eight guidelines are a gross oversimplification. There is no universal requirement for water intake, and your needs will vary widely based on age, gender, body size, health status, and physical activity levels. Numerous environmental factors, such as high temperature and humidity levels, also influence water needs. (3)

It is difficult to estimate an exact amount of water needed for an individual, so thirst should be used as a general guideline for most individuals. In other words, if you are thirsty, drink, and if you’re not thirsty, don’t force yourself to drink simply because you believe it to be a healthy practice.

Additionally, the eight cups a day recommendation typically does not account for the water content of food. Many Paleo staples are surprisingly high in water; besides just fruit and vegetables, foods like yogurt, salmon, eggs, and potatoes are about 75% water, and four ounces of broiled salmon provides about one half cup of water. (4) If your diet is full of water-rich fruits, vegetables, and animal products, you may not need as much liquid water as you think. And if you’re eating soups or broths, that volume should certainly be counted towards your daily fluid intake.

Let thirst be your guide

Thirst is a sufficient indicator for most people of hydration status. From an evolutionary perspective, thirst has done a pretty good job of enabling us to survive as a species. While many believe that thirst is an indicator that a person is already dehydrated, this claim has not been substantiated by any research. (5) Thirst actually begins when the concentration of blood, an accurate indicator of our state of hydration, has risen by around two percent; experts generally define dehydration as beginning when that concentration has risen by at least five percent. (6) So while thirst is a good indicator that a drink would help maintain good hydration, it doesn’t necessarily imply dehydration.

Exceptions to thirst guiding hydration might include athletes engaged in exceptionally strenuous activity, when dehydration is far more common and adequate rehydration is essential to athletic performance as well as good health. Drinking plain water can improve performance in endurance exercise, but there are further performance improvements when carbohydrate and electrolytes are added. (7) Sodium should be included in fluids consumed during exercise lasting more than 2 hours, and is beneficial for aiding rehydration for anyone engaged in moderate activity. (8)

People with health conditions that affect their thirst, such as diabetes or kidney disease, may need more precise estimations of fluid needs on a daily basis. Excessive thirst is a symptom of hyperglycemia, among other diseases, and not necessarily an indication of dehydration.

If you find yourself having constant thirst despite drinking regularly, you may have a serious condition that needs treatment from a medical professional. Again, individual needs will vary greatly, so pay attention to your own health.

What should you be drinking?

Pure water is probably good enough for recreational athletes engaged in mild to moderate activity. Those doing intense training or those who sweat excessively, however, will need electrolytes in addition to water, and possibly even sodium tablets. Sodium is essential to avoid hyponatremia, a serious condition caused by a lack of salt in the blood, leading to water imbalance and water build-up in the brain. (9) Therefore, sodium is one of the major electrolytes that is essential to include in a rehydration beverage following strenuous exercise.

There are many great natural alternatives to commercial sports drinks for replacing electrolytes during and after strenuous exercise. Bone broth is full of minerals such as calcium and magnesium, which can help with muscle contraction and relaxation, as well as amino acids for improved muscle and joint repair, making it a great choice for athletes. Coconut water has a good mix of electrolytes and simple sugars to aid in sports performance, though extra salt may need to be added to some brands that are lower in sodium to optimize rehydration.

Homemade sports drink recipes can be found around the web; a great one can be found on Wellness Mama’s blog. Fermented pickle or sauerkraut juice is another great way to boost hydration, especially for those who need the extra sodium and electrolytes. An added bonus of drinking these fermented juices is that they also contain probiotics to aid gut health. Even just adding a pinch of sea salt to your water bottle should be sufficient to aid in rehydration after a trip to the gym.

Take home message: Drink what you want!

The best advice I can give when it comes to water consumption is let your thirst be your guide, and adjust your fluid intake depending on your lifestyle and environment.

If you are relatively sedentary, live in a cold climate, don’t sweat much, or eat water-rich foods, you probably don’t need to be drinking eight cups of water a day. There’s no evidence to support those recommendations, and forcing down excess water throughout the day is not only unnecessary, but can cause damage if done too frequently. For most people, the body is its own best guide.

What is your favorite way to rehydrate? Do you have any beverage recommendations that I didn’t mention in my article? Share with us in the comments section!

147 Comments

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  1. Thanks for the important comment on elderly patients. My mother had absolutely no thirst reflex and we took her to the ED more times than I can count to be rehydrated. One doc said: her urine looks like Cabernet. I asked her primary care doc if we could set up a drip at home (she had a skilled caregiver) and he rolled his eyes at me. What a waste of time, resources…and life.

  2. Great article Chris. I have one suggestion for anyone that is ill or looking for an ideal and exact method for keeping their body properly hydrated. Get a refractometer and measure your urine brix. This is a measure of your urine concentration and it can be an extremely helpful guide in determining fluid intake. I would even go as far to say that it may be one of the greatest health tools available since proper hydration has so much to do with overall well being and optimum body functioning. Sometimes the body’s own fluid intuition can be off and a refractometer shows you how to optimize it.

  3. As I get older and older …. 94 now …. I am more and more concerned that my body may not be telling me when to drink . As a result I drink mostly when I am thirsty as Chris says. I take no medications of any kind, prescription or OTC. Therefore, there is no influence there. The engineer in me tells me to note what makes me thirsty. I find that excessively sweet things and escessively salty things will make me very, very thirsty. For me, there is treachery in foods. I get apprehensive when eating out, or anywhere when others are doing the cooking since excess salt easily hidden, and it will make me very thirsty hours later when I get the AHA! moment. Yes, Chris, listen to your body and don’t try to fool your body either.

    • Your 94 and clearly doing what right. Keep it up. That’s fantastic. I have a 93 year old in my house and she eats and drinks what she wants which doesn’t include pop Coffee tea orange juice tomato juice and water. I know I won’t live to be 93 but clearly not overthinking everything and no Internet use has aided alot of elderly people to live long healthy lives. If any of us younger folk even make it close to their age, it will be because they chose to eat and drink in moderation and avoid every fad that passes by.

  4. Chris,
    Thanks for a nice perspective. I already printed out some of your info to two patients this morning. Currently reading Waterlogged by Tim Noaks which goes down that rabbit hole a bit more. You can hear him interviewed by Ben Greenfield a couple of times as well. Your efforts are greatly appreciated.

  5. Often I add some flavored stevia to my drinking water. Most days, I drink about 6 8 oz glasses and that seems sufficient. The stevia just makes it feel like a treat and does not add or take away fromt he value of the water, to the best of my knowledge (google Sweet Leaf or Wisdom Natural Brands for info on the flavored stevia). If anyone knows a good reason why not to use it, please comment.

    • “If anyone knows a good reason why not to use it, please comment.”

      I think it’s a good idea to get used to the fact not everything we eat needs to taste sweet. Take some time to enjoy bitter, sour, spicy, etc.
      I know for me, any time my food paradym shifts, my palate needs a little time to shift also. Just like shifting from hot showers to cooler showers, there is an ajustment period and for me the stevia would prevent the transition to being able to enjoy fresh lemonade with no sweeteners in it.

  6. I feel like when I was pregnant, I needed a GALLON of water a day ;o) This is a really interesting article. Thank you for all the research you provide!

  7. One last thing: I’m also finding the folks have lost their thirst – meaning they’ve gotten so dehydrated that their body doesn’t even signal thrist anymore… until they get properly hydrated and then their thirst mechanism comes back. I’ve read and experienced myself that by the time I’m thirsty I’m already on my way to being dehydrated. So for myself and the recommendation I give my clients is to drink a minimum of 50% of their body weight in water a day, split into 3 portions to be drunk over a period of time between meals – before breakfast, between b’fast and lunch, and between lunch and dinner. Minimizing fluids before bed. Add another 16 ounces for any coffee, alcohol or (God forbid) soda, which I also work to help people wean off. Add another 32 ounces for strenous workouts. This rule of thumb
    seems to work really well for everyone.

    • I don’t get your rule of thumb. I weigh 152 lbs. Should I drink 76 lbs of water a day? Or do you mean take one-half my weight in pounds and drink that number of ounces of water?

      I take Chris’s point that a universal rule such as yours is not really necessary. But, I think people need to be sensitive to the possiblity that as individuals they may be prone to dehydration and their thirst mechanism may not be functioning well enough to rely on it for prevention. Those people should adopt a rule of thumb.

    • Hey Shaya, it seems you’re trying to equate the folks who frequent Mr Kresser’s blog with the overweight, undernourished, junk food eating general public. I’m willing to bet a fresh organic glass of coconut juice that anyone who frequents this blog is pretty far from dehydation.

    • I totally appreciate your opinion, which comes from direct experience. Thank you very much for sharing your wisdom. I am an example of precisely what you describe.
      I need water and lots of it. I only discovered this recently, that i was so dehydrated and had no real thirst and yes hungry all the time.
      So basic, yet so overlooked.

  8. As a nutritional counselor, I am finding that many chronic health issues are relieved with proper hydration, and that most of my clients are coming in dehydrated. I think this relates largely to the amount of diuretics people are drinking – everything from coffee first thing in the morning and many times continued through out the day to soda and other concentrated sugary drinks to the cocktails and wine they drink in the evening. People are quite dehydrated, and often need to drink more than 8 glasses of water a day to make up for the loss they are experiencing through the other beverages they are drinking. There is a downward vicious cycle of becoming dehydrating, losing energy and reaching for the quick energy of coffee or soda or sugar and then becoming further dehydrated. So I don’t take hydration lightly in my practice, in fact water and proper hydration throughout the day is one of the first places I start. Especially with high blood pressure, urinary issues, energy issues, mood issues, digestive issues, sleep issues, chronic pain, etc. It’s all related to chronic dehydration in my opinion. Certainly one needs to know how to properly hydrate their unique body, but I’m suprised to read that you shrug it off as an important player in the health issues people are facing today. I really appreciate your blog and often recommend it to my clients, but this article makes me a bit nervous. Our primordial hunter gatherer ancestors may have been properly hydrated through food and the occasional sips of water from the spring, but today’s busy, coffee and wine fueled society is a different animal that needs, in my opinion, to really watch their hydration vigilantly according to their diet and lifestyle.

    • I think you have your information wrong. While you could certainly argue that they do not make you more healthy, coffee, soda and sugary drinks are not diuretics! That really is an old, unfounded belief. Please check the research because it shows that only in excessive amounts does caffeine have a diuretic effect. Also, high blood pressure is not related to chronic dehydration and while adequate hydration is necessary, be careful pushing too much water on those with high BP. If they have an undiagnosed cardiac condition, that can cause congestive heart failure.

      • Thank you! I was thinking the same thing and have always believed that the 8 by 8 water concept was nuts. I have always been one to drink about half the recommended amount of water and my urine has always been very pale yellow and my BUN and creatinine has always been good. I’m a nurse and don’t have time to pee much less drink.

  9. Both coffee and tea are diuretic, this means they will dehydrate the body.
    Also if you feel hungry drink a glass of water as the brain confuses thirst for hunger.
    Fruit juices can’t substitute for water either as the body has a hard time properly metabolizing sugar. To correct the reaction to this, the body has to surrender water from the extracellular fluid.

    • Yes, it does naturally. Typically, coconut water contains 2-3 times more potassium than a banana and always includes a small amount of sodium as well. During exercise, these are typically the only two electrolytes your body really needs. Extended exercise sessions do place extra stress upon the body which then depletes other electrolytes, but overall, potassium and sodium are the two most important to be consumed during exercise and should always be consumed together, if possible. Their uptake in the body is synergistic and works much more efficiently if they’re paired.

  10. Thanks for another great article Chris, every time I read one of your articles I see the clear concise execution of common sense and scientific backing that makes your work very informative and it’s a great recourse for my clients (im a PT) aswell as me. With the regards to the water consumption I would definitely agree and say that the body and mind are the best indicators as to whether we need more (or sometimes less). I’ve seen water consumption almost cure feelings of empty thoughts and depression over night , it truly is the mineral of life 🙂

  11. @Carol – I understand that you do not really benefit from drinking a freshly juiced drink unless you consume it with a saturated fat as you are unable to absorb the minerals etc properly without the fat. Is this correct?

    • @Marrat. Where did you get that nonsense from, WPF?. You dont need fat to absorb most minerals expecially electrolites, like sodium potassium, etc, its just share bro science. TO consumer sat fat with juice to get your minerals absorbed its like adding protein in your water to get water absorbed :D. Can believe ppl right such things. You may absorb better some fat soluble vitamins like carotene consuming with fat, but not minerals.

      • The slam against Weston A Price is unsubstantiated. If our nation would have followed the health wisdom and science of Dr Price ( and the organization bearing his name) we would be the healthiest people in the world .. We have gone an opposite direction and are asa result -the least healthy.. I suggest you brush up on his and their writings and research.

        As far as “juicing” goes – where did one get the idea that it is even good for you.. yet another infommercial-based decision. Too many late nights awake in the hotel room?

        Juice= concentrated fruit ( w/out any fiber) = SUGAR ; which is THE main culprit in modern disease. (And that’s not even considering the other poisons)

        All modern fruit is bred for high sugar content, so unless you are picking/buying wild fruit ( like wild blueberries), it is a losing battle to try and show the health advantages of fruit in general.

        Good starter article on it-
        http://www.marksdailyapple.com/juicing/#axzz21LqnSU5Z

        “If the govt says it’s good for you… RUN !”

        • Ummm…juicing for most people means vegetables with a very very small amount of fruit. What are you talking about?

          • Gotta watch those Weston Price sycophants, they’re zealous!

            There is far more to juicing than people who don’t juice know. The non-juicing community always uses a bottle of high fructose commercially prepared crap as the straw man.
            Funny how many anti-juicers take vitamin suppliments. What’s up with that?
            Lastly, Mark Sisson is my most favorite nutrition and exercize guy, but even he drinks unfiltered tapwater. I sure don’t.

  12. Also wondering about adding something like Emergen-C to water. I take a hot yoga class and started adding that in. Does it have everything I need or should I make a homemade mixture?

    • You could instead just eat an orange or two since Emergen-C does very little to your system except severely overload it with vitamin C. It’s good that vitamin C is water-soluble so you excrete anything your body can’t absorb, otherwise you could get C-vitamintosis extremely quickly due to build-up in adipose cells.

    • Actually, if you read the label of Emergen-C, you’ll see it has Fructose listed as the first ingredient, and 6 grams of sugar total. I’d avoid it for that reason alone. I’d just drink water.

  13. I was wondering about Brad’s question too. Regarding drinks, I do drink water upon rising but I’m also trying to have one fresh juiced green drink – all veggies with 1 granny smith apple per 2 servings.

  14. No quibble with the gist of this, but some huge caveats:

    In the exercise guide “Body by Science”, was written by Dr. Doug McGuff, M.D., an emergency room doctor. In a discussion about adequate hydration when exercising, he had this paragraph:

    The importance of adequate hydration is seen daily in emergency rooms throughout the world, particularly with elderly patients, whose thirst mechanism is impeded. A common tipping point in their becoming ill is inadequate hydration, which impedes the ability of the bloodstream to deliver sufficient oxygen to the tissues. Dehydration results in a constriction of blood volume to the point where they can no longer perfuse their tissues with sufficient oxygen, causing them to become acidotic. Once this happens, the metabolism becomes almost glycolytic, producing lactic acid. At the same time, a consequence of acidosis is a drop in blood pressure, resulting in acute sickness. Many such elderly patients who arrive at emergency rooms from a local nursing home look as if they are dying, but after the attending physician administers a liter of IV fluid over the course of two to three hours, they awake, completely alert, and appear completely well.
    [end quote]

    My Dad, an active and healthy 89-year old, has had several spells that were scarey, and led to discussion of whether activities like driving might need to be curtailed. They are thoroughly controlled by a recognition that he needs to drink water even though he is not thirsty. My then 87-year old father in law lay near death (so it seemed) in an emergency room, with no treatment for hours, until the Sunday morning crew showed up at 8 and gave him an IV drip. By 10AM he was back from the dead and raring to go. Elderly people should not trust their thirst mechanism, especially if they are popping all kinds of pills as most of them are.

    A failure to understand this is putting a needless strain on emergency rooms, and adding to the woes of our seniors with an easy as pie fix available for no cost. Understand that the thirst mechanism can be faulty with age and medications.

    To avoid cramping if an athlete is prone to that, early and plentiful hydration is needed starting well before the exercise and thus well before the body is sending thirst signals. This is good too for osteoarthritis if exercise brings on pain or stiffness, as hydration adds a little extra bounce to the cartilege.

    • I agree that relying on thirst is not always adequate (though it should be under ideal circumstances). I think modern, stressed out humans are often a bit out of touch with their bodies’ signals. I, for one, often find myself drinking very little water for a few days because I am not thirsty. When I notice this and make myself drink some extra water, I almost always feel better.

      • I third that idea as I know from personal experience when I was studying during university that the long hours, focus and stressed lifestyle barely ever made me think of drinking. Relying on my body’s signals simply wasn’t good enough, as again we are in general as a society today completely disconnected from our body’s signals, nature, each other, etc… I would go daily on a juice box! (yes hard to believe when I think back now) for days and not think anything of it. It wasn’t until I took drinking water seriously and properly “rehydrated” my body that I knew what it meant to “need” water and have the body ask for it specifically each day.

        So yes, I agree that the numbers are artificial and each person will need a different amount, but I don’t think the importance of getting high quality water daily can be over emphasized for optimal health.

        • If you are “normal”, “healthy”, thirst is the best indicator to measure if fluid intake is needed.

          However, as Chris pointed out, if you are very physically active or suffer with chronic health conditions, your own body may not be the best judge or form of measure regarding fluid intake.

          Even fluid “input/output” ratio may not be valid if the person is retaining water within the body (abdominal distension, foot/leg edema, etc.)

    • What do you all think of Hexagonal water? I have been researching the “Vitalizer Plus” (VitalizerPlus.net) for a while and it intrigues me lots. It is a wee bit pricey, but if it’ll feed my body more nutritional water, I may go for it. That vs juicing? Ur thoughts, please.

      I have “Body by Science” downloaded on my Ipad and am in the process of reading it. Very good read.

  15. I completely agree with the ‘drink when your thirsty’ statement. Typically I drink water that has gone through a reverse osmosis treatment. I add essential salts back to this water using commercially available products like Concentrace. Do you think salts should be added to RO water? Is there validity to the claim that because RO water has virtually everything removed it is more reactive and leaches your body of essential salts?

    • I do RO and I also do concentrace minerals, but I DON”T do the concentrace minerals BECAUSE of my RO filter.

      Most of the minerals in the tap water cannot be adsorbed by or bodies, and some of the TDS in tap water is caused by metals you don’t want anyway. One serving of greens will give you more bioavalable minerals than several days of tap water.

      The whole RO/mineral scare hocum is led by idiots that think flourine is beneficial to your health. We know better than that.

  16. I often wonder if high consumption of tea (orange pekoe) or coffee or fruit juice is considered part of the necessary daily water intake. And, does it count for ultrasounds when they ask you to drink volumes of water?

    • All of them contribute to the total volume of fluids you take in during the day. Remember, however, that fruit juice contains sugars.

        • Only in large doses. Small to moderate levels of caffeine consumption do not increase diuresis and therefore, do not negatively impact overall fluid balance.

    • I was wondering the same thing Brad. That is how I have always gauged my hydration levels. I have heard that urine should be very light yellow ideally. Totally clear means too much water, but very concentrated yellow means not enough (unless you’ve just taken a round of B vitamins).

    • If your urine is clear, you’re actually overhydrated. The general consensus for proper hydration is urinating once every 60-90 minutes and/or your urine is ever so slightly yellow, neither clear nor fully yellow (and not radioactive yellow due to excreting excess water-soluble vitamins your body cannot absorb). However, be aware, foods and drinks can also influence urine color directly, regardless of fluid intake.

      You can use the following chart as a (very) rough guide: http://flowingdata.com/2012/02/17/urine-color-chart/ . “Optimal” typically looks like a faint yellow.