There is no science that backs up the popular claim that you should drink eight glasses of water a day, and there never had been, says Aaron E. Carroll, an Indiana pediatrician.
Carroll, who previously co-wrote a research paper debunking the common myth, wrote an impassioned article for the New York Times in which he explained yet again that the popular notion is simply not true.
"Many people believe that the source of this myth was a 1945 Food and Nutrition Board recommendation that said people need about 2.5 liters [8 glasses] of water a day," he wrote. "But they ignored the sentence that followed closely behind. It read, 'Most of this quantity is contained in prepared foods.'"
He adds that water is in just about everything, so there isn't a huge reason to drink a ton of extra water. Besides fruits and vegetables, water is also plentiful in juice, beer, tea and coffee, and the idea that these drinks dehydrate is also not true, reports Science Alert. The amount of water that they contain is far higher than any diuretic properties in the drinks, so they are perfectly fine for hydration.
Additionally, it might not even be true that drinking extra water has added health benefits for people who are otherwise healthy. "Reviews have failed to find that there’s any evidence that drinking more water keeps skin hydrated and makes it look healthier or wrinkle free," Carroll explains.
There really is no evidence to suggest a particular water intake recommendation. In fact, our bodies are quite adept at telling us when we need to increase our water levels, he says. While many people claim that we feel thirsty after it is "too late," our bodies actually detect thirst when our blood concentration has risen by less than two percent, "whereas most experts would define dehydration as beginning when that concentration has risen by at least 5 percent," he says.
These recommendations are for sedentary, healthy adults, so anybody who works out a lot or faces an illness or extreme heat might find that they need to drink 8 glasses a day or more.
Ultimately, the only thing that we know drinking extra water causes is regular bathroom trips.