This is the most well-known but laughably arbitrary rule of thumb that was hammered into most of us since childhood. In fact, Professor Heinz Valtin went as far as to pen a paper published by the American Physiological Society on the lack of scientific evidence behind the popular axiom.
The truth is, your actual needs can be more than either glasses, or less, and there’s no magic number, and the amount changes every day depending on your size, weight, ambient temperature, daily activities, and, more significantly, your food.
So, how much water should we drink? Before all this science, people relied on a pretty fine-tuned, reliable mechanism to make sure they were getting enough water. It’s called thirst, and you may have heard of it. Drink enough to satisfy your thirst, and that’s good enough.