It’s a myth that you need to drink 2 L of water—that’s around eight glasses—every day in order to maintain good health. The bad news is you probably need far more, but the good news is you’re already consuming more than you realize.
In fact, on average we need to consume around 6 L a day, but that doesn’t have to come just from drinking water. Any beverage we drink contributes to the total, as does the food we eat—especially fruits and vegetables—and the moisture in our environment, which is another source of liquid.
The optimum intake depends on our age, weight, location, level of activity and sex. And it varies enormously around the globe, with some people consuming just 1 L a day, say researchers from the University of Wisconsin-Madison.
But the idea that we need to be consuming 2 L of liquids a day is a myth that isn’t supported by science, the researchers say. For one thing, most people don’t take into account the tea and coffee they drink and the water that’s in their food, and both count toward total intake.
To find out our true liquid consumption, the researchers used trackers on 5,604 people in 23 countries, aged from 8 days to 96 years, to assess their levels of “water turnover,” the amount of water used by the body every day.
The amounts the participants consumed varied enormously and depended on age, sex, outside temperature and physical activity.
It’s complicated, and just telling people to drink eight glasses of water a day is simplistic and could be interfering with the body’s sophisticated management of water. The body urinates out the water it doesn’t need and triggers thirst when we do need to drink.
Consciously drinking more just to follow the stipulation of a myth is a little like breathing more simply because oxygen is good for us, the researchers say. In fact, drinking too much water can be dangerous and could trigger hyponatremia, a life-threatening condition in which the kidneys start diluting the sodium content of blood.
Science, 2022; 378(6622): 909–15