Put down your emotional support Hydro Flask.

The widely held belief that humans need to drink eight 8-ounce glasses of water a day — also known as the 8 x 8 rule — is simply not true, a new study says.

Instead, water requirements vary by individual.

A recent study published in the journal Science found that the amount of water that people need to consume varies widely.

“The science has never supported the old eight glasses thing as an appropriate guideline, if only because it confused total water turnover with water from beverages and a lot of your water comes from the food you eat,” said study co-author Dale Schoeller, a nutritional sciences professor at the University of Wisconsin–Madison who’s studied water and metabolism for decades.

The study, he said, is the most accurate and comprehensive research on hydration and the human body to date. More than 90 researchers contributed to the report, which measured the daily turnover of water of more than 5,600 people from 26 countries — ranging in age from eight days to 96 years old.

“The science has never supported the old eight glasses thing as an appropriate guideline,” lead researcher Dale Schoeller said.
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“This work is the best we’ve done so far to measure how much water people actually consume on a daily basis — the turnover of water into and out of the body — and the major factors that drive water turnover,” Schoeller said.

The research found that water consumption varies widely around the world, with daily averages ranging from about four to 25 cups a day.

According to the study, water needs peak for men in their 20s, while they remain level for women from the age of 20 to 55 — but only vary by about two glasses for each gender, with men requiring more.

child drinking water
The study found that the amount of water a person does and should consume a day varies widely by a large number of physical and environmental factors.
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Physical activity level and athletic status contributed to the largest differences in water turnover, followed by sex, the Human Development Index and age.

The lower a country’s Human Development Index, the more water a person goes through in a day, with hunter-gatherers and farmers in developing nations having a higher water turnover than those in industrialized economies.

Doubling the energy a person exerts every day will increase their expected turnover by about four glasses. About 110 more pounds of body weight adds about three needed cups a day and a 50% increase in humidity in a person’s environment pushes use up by nearly one cup.

In the end, the study did not give a suggested number of glasses the average human should consume per day.

“The variation means pointing to one average doesn’t tell you much. The database we’ve put together shows us the big things that correlate with differences in water turnover,” Schoeller noted.

Schoeller has been studying water and metabolism for decades; his lab pioneered the “labeled water” method used by the study to analyze human hydration and water needs.

Subjects drank a measured amount of water containing traceable hydrogen and oxygen isotopes — distinguishable chemical atoms.

He explained: “If you measure the rate a person is eliminating those stable isotopes through their urine over the course of a week, the hydrogen isotope can tell you how much water they’re replacing and the elimination of the oxygen isotope can tell us how many calories they are burning.”

Newborns turned over the largest proportion of water — replacing about 28% of the water in their bodies every day.

Experts hope the study will improve the ability to predict more specific and accurate future water needs as the world struggles to manage the increasing threat of climate change.

Lead author Dr. Yosuke Yamada, section head of the National Institute of Biomedical Innovation, Health and Nutrition in Japan, said: “Determining how much water humans consume is of increasing importance because of population growth and growing climate change.

“Because water turnover is related to other important indicators of health, like physical activity and body fat percent, it has potential as a biomarker for metabolic health.”

Last year the UN warned of a global water crisis with many cities in the US already struggling to supply clean drinking water to their citizens.

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