No Scientific Proof That You Need 8 Glasses of Water per Day, This Is How Much You Really Need

Drinking eight glasses of water per day isn’t backed by experts. It’s just someone’s antiquated philosophy that keeps being regurgitated.
8 glasses of water

You have perhaps heard that eight glasses of water, or roughly half a gallon (2 liters), should be drunk every 24 hours. This assertion has gained widespread acceptance. But is it really just a myth or a science-backed fact? In this article, we’ll go into deep dive regarding the “8 glasses per day” recommendation, where it came from, and how much water we really should be drinking per day.

The making of the “eight glasses of water per daymyth

The recommended eight glasses of water per day has been around for years. But the idea does not really make much sense when you consider it. No matter how boisterous he or she may be, a 6-year-old primary school pupil does not need an equal amount of daily fluids as a 25-year-old roofer. Hence, it may not be surprising to hear that this purported “law” of eight glasses of water per day has no scientific foundation.

Vaso con agua, Madrid, España, 2021 01 by Benjamín Núñez González under CC BY-SA 4.0

So from where does the eight glasses of water per day come from?

Vincent Priessnitz, an Austrian peasant farmer who was reputable for using wet bandages and drinking a lot of water to recover after suffering a severe accident, is credited with the idea that we should drink lots of water. In the early 19th century, he went on to popularize the hydrotherapy “nature-cure” movement. Drinking and bathing in cold water were advised as a cure for several ailments. Patients of Priessnitz were instructed to consume an astounding 12 to 30 glasses per day.


While Dr. Irwin Stillman’s well-known 1960s diet is frequently cited as the originator of the more recent idea that we should drink eight glasses per day, the US Food and Nutrition Board actually came up with the idea first. In 1945, the Board suggested that US citizens should drink 1 ml for every calorie of food consumed. This equated to eight 8-ounce glasses for a person who consumed roughly 2,000 calories per day.

Stillman’s 1967 book “The Doctor’s Quick Weight Loss Diet,” a low-fat variation of the Atkins diet, was a far bigger success, and his diet called for the dieter to consume at least eight 10-ounce glasses of water each day in order to lower the level of ketones in their blood.

Fredrick John Stare, an American nutritionist, was the following well-known figure on the scene. He co-wrote the 1974 book “Nutrition for Good Health,” in which he recommended that an adult should drink “somewhere between six and eight glasses per 24 hours. And this can come in the form of beer, soft drinks, coffee, tea, milk, etc. Fruits and vegetables also make good sources of water.


Factors influencing optimal water intake

Eight glasses of water each day may be enough for some people but may be too little for people whose daily water needs are incredibly individualized. Generally, one must drink enough water to replenish the fluids lost through perspiration, respiration, defecation, and urination. This depends on a number of different things.

  • Exercise. Any activity that causes perspiration calls for more water intake. Water should be taken before, during, and after a workout.
  • Body weight. People with more considerable body weight should consume more water.

  • General well-being. If you have a fever, vomiting, or diarrhea, your body will lose fluids. A higher fluid intake is also advised for those who currently have or previously had kidney stones and bladder infections.
  • Environment. It would help if you drank more fluids when it’s hot or humid outside and you’re sweating. Dehydration also occurs at high altitudes. Even while your body requires water, the cold weather makes you less thirsty, making the issue worse.

  • Breastfeeding and Pregnancy. Expectant or nursing mothers should drink additional water to stay hydrated.

Sources of water

Fredrick John Stare has already mentioned that there are other ways to stay hydrated besides drinking water. Drinks like milk, fruit juice, and sodas also count, but you should be aware of how much sugar is in them, as drinking only sodas have detrimental long-term health impacts. Contrary to popular assumption, caffeinated drinks like coffee and tea can, when taken in moderation, also add to your fluid intake.

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Unfortunately, alcohol is your worst choice because it suppresses a hormone called vasopressin that aids in water retention, despite the fact that mildly alcoholic beverages like beer might count toward your hydration needs. Last but not least, while you metabolize nutrients, a little amount of metabolic water is also created within your body. For every gram of glycogen, the body breaks down, about 3 g (0,105 oz) of metabolic water is released.


Knowing whether or not to drink water

In theory, thirst will let you know when you need to drink more water. This should occur when you begin to experience dehydration and have lost about 2 percent of your body weight in water. Most experts define dehydration as starting when you have lost 3 percent or more of your body weight. The more your level of dehydration, the more thirsty you will feel.

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Generally speaking, drinking when you’re not in the mood is unnecessary. It takes more physical effort to drink when you don’t feel thirsty than when you do. Especially if you have 8 glasses of water before you.

Several studies that have used brain imaging also demonstrated that drinking more water than necessary might be unpleasant.


As humans, our brain makes every effort to prevent “social polydipsia,” a chronic overdrinking attitude brought on by “the misconception that taking eight 8-ounce glasses of water per day is needed for optimum health.” Doing so could cause your ureter or bladder to expand. In the worst case scenario, it can lead to renal failure.

Is drinking too much water dangerous?

It’s generally not dangerous to consume too much water. You will dispose of it through your urine. Your kidneys’ major job is to balance out water intake and loss. Within 40 seconds, kidneys can respond to any disturbance in the water balance, whether it is caused by overhydration or underhydration. If otherwise and you end up drinking too much, you’ll start holding onto water, and more of it will build up until you start to notice your feet swelling. At this point, it is advised you see a doctor.

The takeaway

The major lesson from this is to always drink water when you’re thirsty. Or eat some watermelon instead. Otherwise, don’t. Just relax; there are no hard-set targets to meet—especially not eight glasses of water per day.


Featured image credit: 8 glasses of water by

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