How Much Water Should You Really Drink Each Day?

Contrary to popular belief, not everyone needs to drink eight glasses of water a day, according to a new study published in the journal Science.

Researchers tracked daily “water turnover”—the amount of water consumed and lost by the body—in more than 5,000 participants. They found that the water turnover rate was typically the highest among men aged 20 to 30 and women aged 20 to 55. Other factors like body size, physical activity level, and climate can also affect individual water needs.

According to Yosuke Yamada, PhD, the lead researcher of the study, men need to drink about 1.6 to 1.8 liters of water per day and women need about 1.4 liters, based on the research team’s calculations. Those equate to about six to seven cups of water per day.

In 1945, the Food and Nutrition Board of the National Research Council said that adults need about 2.5 liters of water daily in most instances. An ordinary standard is 1 milliliter for each calorie of food, and most of the water intake can come from prepared foods. The recommendation was misinterpreted into the conventional advice to drink eight 8-ounce glasses of water per day.

The new findings suggest that the recommendation for water intake is too high and that there’s no one-size-fits-all approach to water consumption, Yamada said.

Men in their 20s had among the highest water turnover rates, which suggests they had among the highest drinking water needs, he said. Men also had higher water turnover rates than women across all ages.

In addition to sex-based differences, the study found that people living in hotter climates had higher rates of water turnover than those living in more temperate climates. People living in poorer countries had higher levels of water turnover than those in developed countries, and athletes also had higher turnover rates than those who exercised infrequently.

So How Much Water Do You Really Need?

High water turnover rates don’t necessarily represent good hydration, though.

Jodi Dunmeyer Stookey, PhD, a nutrition epidemiologist focused on water intake and founder of Water & Hydration Translational Epidemiological Research (WAHTER), told Verywell that the study provides useful insight into how much water people do consume, but not how much they should consume to be healthy.

“The study just shows a lot of variability,” Stookey said. “Some people don’t need that much, but some people do and they need even more than that.”

The researchers did not measure the benefits or risks associated with consuming too much or too little water, which would be necessary to make a recommendation, she added.

“The recommendations that we make are supposed to keep people healthy so you don’t get sick tomorrow, or get diabetes or chronic diseases over a few years,” Stookey said. “I feel really sad seeing in the press that ‘you don’t need to drink water.’ The study is not saying that.”

“It’s a beautiful study—I just feel like they’re plucking at straws a little bit,” she added. “The focus should be that it’s very individual what you need to drink.”