It Is Not Necessary To Drink At Least Eight Glasses Of Water A Day To Stay Properly Hydrated

Myth: You should drink at least eight glasses of water per day to stay properly hydrated.

Probably one of the most widely spread urban health myths of all time is that the average person needs to drink at least eight 8oz glasses (approx. 2 liters) of water per day to remain properly hydrated. Popularly known as the ‘8×8’ (for eight, eight-ounce glasses), this H2O guzzling advice has been publicized by health writers, physicians and nutritionists alike, and often stated as the ‘first commandment of good health’. However, this widely acknowledged recommendation has been proven to lack any scientific basis.

The origins of this so called rule of health are as fuzzy as the medical benefits it’s meant to provide. Some say the notion may have started in 1945 when the Food and Nutrition Board of the National Research Council recommended approximately “1 milliliter of water for each calorie of food,” which would amount to roughly 2 to 2.5 quarts per day (64 to 80 ounces) for a typical 2,000-calorie diet.

Some trace it back even further to as early as the 1700’s with German physician, Christoph Wilhelm Hufeland (1764-1836), who practiced natural medicine and vitalism, and wrote a few books on macrobiotics. In his book titled Makrobiotik oder Die Kunst, he propagated the importance of drinking water that was alive like fresh spring or mineral water. He went on to emphasize the many special curative properties attributed to fresh, cold water, which he said was a “fortifier and vivifier of the stomach and nerves, and an excellent antibilious and antiputrid remedy.” Dr. Hufeland even described his water prescription to drink at least 8 glasses of water a day.

While his book was written in 1796, Dr. Hufeland described a Surgeon General to the King of Prussia, who, from the age of 30, had suffered from “hypochondria, melancholy, heart palpitations, and indigestion.” By following a water diet, “all his complaints disappeared” and he was said to have enjoyed better health the last half of his life than he had during his youth. Throughout the 18th and 20th centuries, the hydropathy water cure was popular in Europe and America, as practitioners encouraged their followers to drink lots of water for healthful and curative properties and to flush out toxins and impurities, showing that the popularly known 8×8 health recommendation has been believed for at least several centuries.

Regardless of its origins though, the 8-glasses-a-day dictum caught on and now up to three out of four adults can recite this bit of health wisdom, with very little clinical evidence to support it. In one such study on this myth, done in 2002, Heinz Valtin, a Dartmouth Medical School physician and kidney specialist, who researched the subject thoroughly, released his findings. He believed that the statement supporting the notion, taken from the Food and Nutrition Board of the National Research Council was grossly misrepresented by removing it from the original context. The sentence that followed the one popularized by the Council stated, “most of this quantity is contained in prepared foods,” which was left out either consciously or erroneously, and led to the false interpretation that the requirement needed to be fulfilled by drinking plain water alone. After 45 years of studying the biological system that keeps the water in our bodies in balance, Valtin concluded that drinking such large amounts of water is not needed at all. He points out a number of published experiments that attest to the capability of the human body for maintaining proper water balance from sources other than directly drinking water which may include drinks such as tea, coffee, soft drinks, as well as other prepared foods. The truth of the matter is that most foods have some water content. For example, here’s a look at the percentage of water content in certain foods- Apples: 85%, Bean sprouts: 92%, Chicken, boiled: 71%, Cucumbers, raw: 96%, Lettuce, head: 96%, Potatoes, raw: 85%, Turkey, roasted: 62% and so on. These and other food sources account for some of the fluid intake needed by our bodies.

The bottom line is that the body does a pretty good job of letting us know when we need more water by making us feel thirsty. The only thing chugging down glass after glass of water is going to do is make you pee more frequently as your body needs to expel the excess liquid. Except in the case of people who have specific health concerns, such as kidney stones or a tendency to develop urinary tract infections, where drinking lots of water can be beneficial, the average person will remain properly hydrated if they simply drink when they’re thirsty.

Bonus Facts:

  • Scientific evidence also debunks the popular myth that by the time you feel thirsty, you’re already dehydrated. A number of scientific studies have confirmed there is no support for this fear. Quite the opposite. Thirst hits long before we’re near risk for dehydration. Specifically, most people’s thirst mechanism kicks in when the osmolality of our blood plasma is less than 2%, whereas dehydration begins at osmolalities of 5% and higher.
  • Valtin found that, among most adults, caffeinated and alcoholic beverages constitute half or slightly more of their daily fluid intake, meaning the average adult drinks a respectable 1,700 ml and this doesn’t include the water from foods and metabolism, which also count. Yet, the medical research indicates that even 1,700 ml may be as much as a full liter more than what sedentary adults actually need to maintain physiological homeostasis.
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  • Nobody still believes me after referring to this article a million times.

    • Daven Hiskey

      @CJ: Join the club. 🙂 Just about every “Common Misconception” article I’ve done here has resulted in numerous people basically saying, “I see all your evidence and data dispelling the myth, but I’m going to ignore it all because when I was little, I was taught it was true.” 🙂

  • Wouldn’t one rather be over-hydrated rather than under-hydrated? It’s the ol’ “better safe than sorry” scenario. Drink more water kids!

  • I hate it when someone amazes us with the “there’s water in food” fact. Guess what? Some foods require more water for the body to process. Don’t rely on food as a source of water.

    • In the context of this article, that fact is presented as a clarification of the origin of this 8×8 myth. It’s not presented as a reasoning to drink no water at all. The fact that there is water in food was ignored by those that propagated the 8×8 theory, which is the basis of its inaccuracy. Eight glasses a day may be excessive because water in food accounts for much of the total water consumption prescribed by the original publication. No one here is saying water in food is the only water one needs. That’s crazy!

  • I was dehydrated and had to have IV tube, 3 bags later, was hydrated. I did not feel thirsty before this happened. I had a bad headache and very tired, even with a nap, didn’t go away, so went to the hospital and then found out I was dehydrated.

    As a body gets older for some, loses the sense of being thirsty. I have to remind myself to drink more water so don’t get dehydrated happen again.

    So, this article is incorrect in saying the body knows when it’s thirsty because its not true for everyone.

    • Sorry to hear about your hydration episode. But most bodies know when they are thirsty. This is true, in general, but no medical advice can be true for every single person. Generalizations are helpful because they apply to most people. There is always a percentage of outliers no matter what the topic, so saying the article is wrong because you, one of tens of thousands of readers of this article, found that one statement didn’t apply to you all the time is like saying the sky actually isn’t blue because you happen to be wearing pink sunglasses. The article is correct, in general, for most people. The article states:

      “Except in the case of people who have specific health concerns, such as kidney stones or a tendency to develop urinary tract infections, where drinking lots of water can be beneficial, the average person will remain properly hydrated if they simply drink when they’re thirsty.”

      …The average person. If you have a health condition that causes your body to ignore thirst and become dehydrated, you’re one of those exceptions.

  • Since the major of the water consumed goes to your head it can cause headaches. For me that happens a lot so the 8×8 rule would actually be bad.

  • Too much water is overkill. Your body rejects it. Excessive amounts can harm the humans, and animals. Water from the tap, and much bottled water contain everything from prescription drugs to hormones, to arsenic and perchlorate (jet fuel, and many other unpleasant things.
    In the early days of this country and in many other places, drinking water was and is flat out DANGEROUS. Settlers drank whiskey and cider rather than risk drinking water filled with harmful germs.
    The fact is humans can survive and thrive perfectly fine without hardly any water and have been doing it for millions of years

  • Everyone seems to be overreacting to this article. I think what you’re trying to say is basically that we don’t have to abide strictly to the 8×8 rule. But that doesn’t mean we must never drink that much water.

  • Hey C.J.- You’re not the only voice crying in the wilderness- I frequently hear both doctors and nurses spouting “conventional wisdom” (read as “blind faith”) supported by word-of-mouth repetition rather than evidence. One thing I have heard is that the osmotic sensing system (like the rest of the body generally) doesn’t function as efficiently with advancing age. Since we rely on our “senses” (there are far more than five by the way) to detect dehydration, this seems plausible as a mechanism for dehydration in the elderly. What do you think? Since ambient temperature and physical state (i.e., exercise, illness, vomiting/diarrhea, etc.) and body mass greatly affect fluid requirements, how could there ever be a “right” amount of water to drink for everyone?
    That conclusion doesn’t require scientific or medical expertise, only a rational analysis – examine the question before attempting to answer it.
    To paraphrase the words of George Carlin- ” some say the glass is half empty while others say it’s half full- I say the glass is too big.” The question itself is bogus. Reducing a complex, dynamic situation to an artificially simple proposition is irrational and foolish. Am I the only one who finds it ironic that in a time when reliable information is so easily available, that so many still blindly believe what they are told by friends, colleagues and the internet rather than investigate it further? Alas, everything is simple to a simpleton! Keep up the good work of dispelling myth and magical thinking.