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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.

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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.

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Join the conversation

  1. I agree with the article in that everybody’s circumstances are different. Weather and activity level are the determining factor. To me drinking before getting thirsty makes as much sense as eating before getting hungry. It will lead to overweight health issues. Our ancestors acted on nothing but thirst and hunger as motivators and I believe that the body knows best. The question should be more about how much attention are we paying toward the sensation of thirst. I know when I am busy at work as a first responder, I don’t always have time to pay attention to my thirst. I will change that by always having water readily available and to make the time to dink when I feel thirsty.

    • So my 79 year old mom barely drinks any water cause she claims it makes her pass urine but she can’t move her bowels so what’s the deal?

      • She is dehydrated and it is causing her bowels to be constipated. And yes she is going to urinate more frequently when drinking more water but that is perfectly okay and it’s good for your body. It helps to rid your body of toxins. Please encourage her to drink!!!!

  2. If I don’t put electrolytes (Nuun tablets) in my water when I exercise (even for less than 30min) I will start breathing heavily, I will want to vomit and faint. If I hadn’t found this out, I would not have been able to get in better shape. I don’t know why this is such a problem for me though, if I drink too much water (especially when exercising) I actually feel a lot worse. I came to the conclusion that water is not that hydrating by itself…

        • You need more salt in your diet. low blood pressure can ce the result of low sodium intake. And if you eat too much salt and not enough water you will have high blood pressure and you would need to increase water intake so you excrete excess salt and normalize your high blood pressure. This is what my Dr. told me. Try himalayan pink salt and never table salt, that happened to me and my soduim levels were low now i feel more hydrated and i also thought water was enough but that is not the case. I stopped eating as much salt as i always did and there is where the symptoms began so everything went back to normal when i increased my salt and kept drinking about six or seven glasses of water a day.

  3. I decided to ‘get healthy’ about a year ago and started drinking 2 quarts of water daily and in about 3 months I was practically bedfast. I thought I was losing my mind and was ready for the bone yard (so to speak). My doctor found that my sodium was in the critical stage and that I could have suffered seizures,
    a heart attack or stroke at any time. I had to go into the hospital for saline solution IV’s and was there for 3 days. So drinking the recommended amount of water (2 quarts) a day can be very dangerous indeed.

    • Twid, something is seriously wrong with your thinking. There is no relationship between drinking a half gallon of water a day and sodium levels. Water does not deplete your sodium. Your failure to ingest adequate sodium was your error; not drinking water.

      • that’s not completely true – it sounds like he was diluting the concentration of sodium in his blood creating a pseudo-hyponatremic environment (leading to his symptoms). He didn’t need more sodium, just less water.

  4. While this information is ‘well intended,’ and as my Grandmother used to say, the highway to hell is paved with good intentions. Everyone’s need for water AND the nutrients needed to absorb that water, can be different, but what is not stated here, is that a lot of people have no idea that they need water because their sense of ‘thirst’ isn’t working correctly.
    Drugs, including common over the counter ones, age, lifestyle, and/or or less than perfect health, can interfere with ‘thirst’ perceptions. If someone is looking for a ‘rule of thumb’ to determine their need for water or other fluids, the color of the urine is a better rule, than ‘thirst.
    If the urine is very light yellow or clear, the body is probably OK, If it the color of apple juice, you are seriously dehydrated, not matter how you ‘feel.’ If it reaches a brown coloring, you need to get to an Emergency Room right away.
    Do not ignore the medium or darker yellow color, because continued dehydration can permanently damage your kidneys, and it also indicates a lower than normal blood volume. A low blood volume coupled with a blood ‘thinner’ (anticoagulant) can spell disaster from what would seem like simple bumps and/or bruises.

    If a person drinks pure water, their body will not be able to absorb (use) it, because other nutrients like calcium, potassium, and sodium, must already be present to allow that water into cells where it is needed.


    • Great comment. I became quite rundown drinking RO water for 2 years, so your comment is accurate.

      • I’d like to know what type of water you’re using now and if you’re convinced that it’s only the water change that’s affecting your sense of being “run down.” I came to this page specifically because I found your comment in a search because of this issue of minerals removed by reverse osmosis water.

        The RO dealers claim that the minerals in water are both minimal and difficult to assimilate and that sufficient mineralization can better be obtained by proper food sources, though that’s rather bogus, failing to recognize the travesty of farm land neglect that (you might think my opinion perversely conspiratorial) I think is deliberate because there has been a deliberate attempt, years ago, to destroy the small farms of good and conscientious farmers with corporations which, I think, are controlled by boards that are illegally manned by the same people who man the boards of the pharmaceutical and medical corporations so that they will have a strong supply of people fed with worthless and overly processed food that doesn’t contain the nutrients for good health.

        Yes, I know it’s hard to believe such a sinister situation could possibly develop but I think it has and was very deliberate and the government, via the FDA, is in full collusion.

        It’s even worse because of the revolving door between FDA management and Monsanto, which is clearly intending to not only attempt to own and control the seed companies of the world but to convert what hasn’t already been converted to GMOs.

        Everyone should understand that the corn crop in the US comes from a GMO seed that is not only saturated with a poison that kills weeds but will produce corn that is non-fertile and will not grow, so that the farmers (now mostly corporate farms who took control of farms in the 80s through criminal (yet legal) machinations and manipulation of the markets and money to put America’s food production in the hands of a few who are not interested in provinding good quality food.

        It’s not only hard to believe; it’s hard to imagine that the evil was intentional and Machiavellian. I’m convinced it was and that the mass of people in this nation are a woefully misled and misguided by the media and educational establishments, which have shaped the government because of the people behind them.

        I encourage you to search and listen to “Norman Dodd On Tax Exempt Foundations” (YouTube) and listen to it several times until you get a good enough handle of the information to be able to inform casual acquaintances because you’ll send the video link to your friends.

        • I didn’t proofread and made too many mistakes. I’d appreciate it if you delete the above post along with this one and I’ll repost after you do. Thank you.

    • So, are you suggesting the reverse osmosis water is likely to not be utilized by the body as well as good quality tap water?

      By good quality, of course I *mean* good quality, knowing that much tap water around the country and around the world is inferior and has high levels of impurities and most people don’t test their water at the tap.

      Thanks for your reply.

  5. My personal belief is that today’s generation is not drinking enough simple clear n clean water these days, my water must go through reverse osmosis . The seniors of today are the worst offenders I have found. They come into our emergency rooms diagnosed as severly
    dehydrated only after the main issue for the real emergency has been established. Seniors having strokes must be monitored on how much clear clean water they are consuming.
    My Mother was severely dehydrated last month until a IV was given to her containg fluids. In just two days her appearance changed dramatically! So, when caring for ‘hard headed’ seniors it best you consult your doc, then go online, find a site geared for seniors who have some specific health issue then be clever in getting them to drink the planets best drink in the Galaxy … ‘cool clear wonderful water’, it may save your loved ones life !!!

    • You don’t get “reverse osmosis” water through an IV. You get salt water aka normal saline. That is why people perk up so much after IV fluids. If you gave someone fluids with too low of a salt content you can actually cause brain swelling. So you’ve actually contradicted your own point.

  6. the saying ‘if you wait till you’re thirsty, you’re already dehydrated’ is as logical as ‘if you wait till you’re hungry to eat, you’re already malnourished’…if you’ve lost about 2% of your bodily fluid balance, you’re thirsty, 5% yes you’re dehydrated.

    ever wonder why humans feel they’re the only ones who have to drink copious amounts of water and ignore their innate thirst cues unlike animals? does your pet dog or cat need to drink to a schedule or carry a pet-sized water bottle?

    • Yes, funny that, I was thinking just the same thing myself – I have had a bloated stomach – can’t get to the bottom of it then I thought a couple of days ago about the amount of water, tea & coffee – liquid I drink – a huge amount! Not necessary & just habit.

      If you think about it, if you are busy at work you can’t be making endless drinks or pouring yourself yet another glass of water.

      Children at school – they have breakfast, a mid morning snack (before Maggie T a 1/4 pint of milk) at 11, lunch with water or weak orange squash. A snack once at home & possibly a drink before going to bed.

      Pets too – absolutely! My dog’s bowl (shared by the cat) is only ever half empty & I change his water maybe every couple of days – when it looks empty or has bits in it!

    • Give you older loved ones salt. It will make them thirsty. I suspect that low salt causes many to not drink enough water.

      And no, I didn’t ever believe the doctors who claimed salt is bad for you and happily heard the “Dead doctors don’t lie” doctor say, “Salt is good for you and won’t hurt you. Season your food to taste.”

      I *know* the medical industry has done great harm to us. If you doubt, think of appropriate keywords,search and learn.

      Like “pharmaceutical fraud” or “ama crimes” or “cancer cures” or “cancer conspiracy” “lies of the medical industry”

      Experiment. enter “magnesium constipation” and consider why webmd.com is the first entry with a warning of the side effects of magnesium and then then enter “magnesium constipation cure” and see all the sites that tell you magnesium is the number one solution to constipation.

      Understand that Google isn’t serving you; they’re serving their own pockets and the billions of dollars they make on advertising is enhanced by cooperating with the wealthy who make their money off the backs of everyday people.

      Spend enough critical thinking skills on Google and you’ll see why some people’s slogan is “Google is evil.”

      Search “fbi pedophilia” and you’ll only see the FBI as the good guys. You’ll have to get very specific with “owen decamp bonacci pedophilia fbi” to discover that the FBI threatened 28 kids that “you’ll go to prison and stay there the REST OF YOUR LIFE if you testify” against the elected representatives that were molesting the kids–but even then you might have to sift through many pages to find the facts. Google is government’s friend, not yours. You should have been able to find it with “fbi threathens pedophile victims” but if you try that, you’ll only find the FBI as the hero, but if the FBI was really the hero, there wouldn’t be 800,000 children abducted every year.

      You won’t find the truth by “fbi threatens 28 kids” either.

      Do the search “conspiracy of silence pedophilia” and watch the video and start searching. The more you search, the more you’ll think, “this can’t be real; this is like a nightmare.” Wait until you see it’s worldwide and the authorities everywhere cover it up. Then ask yourself if we really need atheists with no morals running the government.

      And don’t think I’m suggesting that the men like Obama who say “I’m a Christian” are telling the truth.”

      Our nation is in worse shape than you can imagine and the media is our greatest enemy. They’ve pretended that there is an adversarial role with the government and that is a total lie. The unelected mean who rule the elected men rule the media also.

      • Gary, you and I seem to be very like minded. I don’t believe that these thing are theory anymore. If you don’t mind my asking, where else do you comment? Are there more of ‘us’ out there?

    • Just like people, pets’ sense of thirst diminishes as they age. In the wild, we assume that animals drink when they are thirsty; but it must be remembered that aged animals are rare in the wild.

  7. When I started intentionally drinking more water – and not just when thirstly – I started feeling much better, and my digestion improved significantly.

  8. Let’s see. I drink when I’m…wait for it…thirsty! Honestly. To all the personal trainers, nutritionists, etc. that say if you wait until you’re thirsty to drink, you’re already dehydrated. What kind of a statement is that??? Well, duh. That’s why I’m drinking a glass of water, cuz I’m dehydrated. I remember my mom (and then me) going on diets as far back as the 50s. All diet books came up with this 8×8. #1–it was supposed to fill you up so you wouldn’t eat more food. (Didn’t work). #2–they wanted you to stay hydrated while cutting back on calories for an extended period of time. Electrolyte balancing come to mind. Oh and BTW, back in those days, you never stayed on a weight loss diet longer than 2 weeks. You then ate normally for a week and back to dieting. Unlike today, where you’re encouraged to stay on a diet until you lose the weight. If you’re dieting for an extended period of time, I could see the 8×8 making sense. And exercise. And heat from the weather. And to flush fiber.

  9. I take 25 mg. of hydrochlorothiazide for hypertension and have taken it since I was a teen in combination with other meds. I am now 71. I am very active and box and workout every week. I have noticed that since I have stepped up my workout it takes longer for my muscles to recover. I do stretching exercises but they don’t seems to work with my muscle recovery. Could it be that I am dehydrated from the combination of my workout and the diuretic? I do follow the 64 oz. rule and eat yogurt, fruits and vegetables.

  10. Dear Chris,

    what is your opinion about the recommended liquid intake done by the EFSA for men (over 14 years of age) to drink 2.0L a day and women (>14 yrs) to drink 1.6L? See: http://www.efsa.europa.eu/en/efsajournal/pub/1459.htm

    Their advice came after extensive literature studies and is the official recommendation by the European Commission. The recommended advice is now being advocated to the general public as well as health practitioners.

    Look forward how you see this advice vs your position as to let thirst being once’s guidance.


  11. This is great information that should be more exposed. I too was a victim of the “water solves every problem” myth. Constipated, headache, nausea, overweight, back pain, allergies? Drink more water!! Errrr! What ever happened to just drinking when you’re thirsty? I used to force myself water and wonder why I craved salty foods so much. There is so much push to drink more water these days and yet so little about how we can flush out all the minerals and vitamins our body needs to survive! Thanks for the article Chris.

    • I agree, I think we drink far too much water, I have cut way back, I drink a glass a day these days.

      Plus a mug or two of coffee, a glass of wine every now and then, plus plenty of fruit, and some vegetables, and moisture from the air. My urine is still a lightish color and I don’t go to the bath room all day and all night.

      I met this nutritionist who got me thinking on this. Drink when you are thirsty he said, it makes sense to me.

  12. “For repeat urinalysis after adequate hydration”….Why is it that i need to repeat urinalysis after adequate hydration? I am worried about this, do i have any disease?.please reply me..thanks

  13. Eighty years ago when I was in high school I studied Chemistry. Mr. Chapman, our instructor, made it clear that sodium chloride is a compound and that sodium is a ‘metal’ that combines with chlorine to make sodium chloride, our common table salt. It makes me cringe when I see sodium and salt used interchangeably in discussions in nutrition. You would never really eat sodium; you’d die. But we need common table salt. (I know there are various kinds of ‘salts.’ Potassium chloride is one of them.) So instead of agreeing that we mean sodium chloride when we say sodium, why don’t we use the word ‘salt and agree that we mean sodium chloride?’ What the body with the sodium and chlorine ions in the blood and organs is something else. Outside of the body we take table salt. I have a salt shaker on my table, not a sodium shaker.

    • Table salt contains aluminium to stop it sticking together. I use pink himalayan salt has over 40 minerals.

  14. I’ve always wondered what made the 8 by 8 rule and how it was proven. It never made sense to me that everyone big or small young or old with these masses of different body types would “need” the same amount of water. I’ve also wondered about purity of that water. I know a lot of filters going to a diatomaceous earth to purify and get clean water on a larger scale. Is there an over purifying of water as well? Is it good to have some minerals in your water for your body?

  15. is drinking diet coke during waking hours ,a source of water to help with stopping nite timw leg cramps.?

    • Clark have you ever heard of oxidation? Battery acid? Aspartame? If not I suggest you do some research. Diet coke is one of the worst inventions in the history of humanity! Check your magnesium levels 🙂

    • Leg cramps are stopped by mustard and water, if you drink coke,Pepsi or any other drink sweetened with sugar or sweeteners your asking for leg cramps. Regular yellow mustard stops leg cramps in their tracks. Water helps prevent leg cramps. Any simple or complex sugars add to the problem.

  16. I am 13 weeks pregnant, and everywhere I go, everybody tells me to drink, drink, DRINK! My GP, my OB-GYN, even my husband always reminds me of that (he loves his water). I am aware of the importance of water and I really am trying to meet the daily norm, but it makes me sick. I feel too full, a lot of discomfort, my belly hurts and it makes me go to the toilet so often. At first I thought something was wrong with me, but today I told my husband maybe I was not made to drink so much. I can do half of it, like 4 glasses, but I never manage to do more. Even this feels more than I would like to. I don’t work out at the moment, I take my folic acid for the pregnancy and I eat my veggies. Trying to be a good girl 🙂 Any advice?

    • Racula, the ‘fullness’ can be easily experienced with drinking tap/bottled water. The same was resolved for me when I tried Kangen Water for the first time, it tasted so good that i couldn’t stop! Drinking it will actually make your body wake up! The hydration it provides is much more efficient due to the molecular restructuring. Kangen water is also full of antioxidants and, unlike the traditional chemically treated tap water was a real solution for me. Well renowned medical practitioners such as Dr. Hiromi Shinya recommends drinking this water. He’s a founder of colonoscopy and examined over 300,000 patients both in the US and in Japan. I’m sharing this because it has made a massive difference in my life on many levels and it might be of help to you. If you want any more info email me: [email protected] And all the best!

        • Really? I like to hear people’s discoverys to improve health, and to do new research. That is how you learn !!!

          • If you knew anything about the product that was being pushed, you would understand. Any product worthwhile doesn’t need to be sold under a pyramid scheme.

      • Another promo of a product. I am getting to the point of not eating of drinking anything that does not exist in nature. Eg. honey instead of sugar, full cream milk instead of low fat. Same thing goes for Kagen water or whatever that is. For the most part anything changed by humans is messed up and has some side effect.

    • The reason why your on tells you to drink water is preeclampsia, this disease can kill you and your baby, please keep track of swelling and you blood pressure while pregnant, if you become hypertensive, seek medical attention.

  17. Hi, I was wondering if Diet Cranberry or Diet Grapefruit juices also count as ‘water intake’ ?

      • I would disagree here… especially ‘diet drinks’…and especially if the drinks are pasteurised etc. Nothing can totally replace real water and fresh fruit/vegetable juice from a juicer! So stuff from boxes/plastic bottles, coffee etc. actually does the opposite. It is all oxidising and adds to the free radical damage.

  18. We add Himalayan Pink salt to our water because it’s rich in minerals. Calcium, Magnesium, Potassium, Copper, and Iron just to name a few.

    • I add a tablespoon of a Himalayan Pink Salt brine mix to my 32 ounce glass of drinking water. I have been do this every morning for over a year. The restructured water and salt combination provide optimal hydration. Plus, Himalayan Pink Salt has over 84 minerals.