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Drinking 8 glasses of water per day might be too much, new study says

Published Nov 28th, 2022 12:28PM EST
Woman holding a bottle
Image: Brita/Amazon

If you’ve ever asked yourself how much water you should drink daily, you might have heard that 8 glasses is the magic number. That’s about 2 liters or around 68 ounces of a critical component the body needs. But a new study indicates the recommendation might be wrong.

Researchers say we should not use a one-size-fits-all recommendation, as various factors might impact daily water intake. Age, sex, climate, and exercise are some factors that would alter the guidance. Add to that the water in food, and daily water consumption recommendations might vary significantly for different people.

University of Aberdeen researchers published their findings in Science magazine. They concluded that people need 1.5 liters (51 ounces) to 1.8 liters (61 ounces) of water daily, as the rest of one’s daily intake comes from food.

“The original estimate of two litres a day comes from a slight miscalculation,” Professor John Speakman told BBC Radio. “The water that we’d need to drink is the difference between the total water that we need to ingest and the amount that we get from our food.”

The scientist explained that the 2-liter estimate comes from asking people how much they eat. And people usually underreport their food consumption.

The researchers measured the water turnover, surveying 5,604 people from 23 countries aged between 8 and 96 years.

Participants drank a glass of water containing deuterium, a stable and safe version of hydrogen. That’s how scientists measured the rate of water elimination related to various factors.

Filling up a glass with drinking water from kitchen tap
Filling up a glass with drinking water from kitchen tap Image source: Dmitry Naumov / Adobe

Hot and humid environments, high altitude, professional sports, pregnancy, and breastfeeding are factors that would increase water turnover. Here are some of the findings:

  • men aged 20-35 need 4.2 liters daily (142 ounces)
  • men and women in their 90s need 2.5 liters daily (85 ounces)
  • women aged 20-40 need 3.3 liters daily (112 ounces)

But Speakman explained that people who need that much water would not get it solely from drinking. For a male in his 20s needing 4.2 liters, “about 15% of this value reflects surface water exchange and water produced from metabolism.”

“The actual required water intake is about 3.6 litres per day. Since most foods also contain water, a substantial amount of water is provided just by eating,” the researcher said.

Speakman continued, “This study shows that the common suggestion that we should all be drinking 8 glasses of water is probably too high for most people in most situations and a ‘one-size-fits-all policy’ for water intake is not supported by this data.”

The immediate implication of the study is that we might collectively save water by drinking an appropriate daily amount. But like any new study, more research is needed so we can find better ways to measure water intake more accurately.

Chris Smith
Chris Smith Senior Writer

Chris Smith has been covering consumer electronics ever since the iPhone revolutionized the industry in 2008. When he’s not writing about the most recent tech news for BGR, he closely follows the events in Marvel’s Cinematic Universe and other blockbuster franchises. Outside of work, you’ll catch him streaming almost every new movie and TV show release as soon as it's available.