Hydrate or die, warned Camelbak, the American water-pouch-in-a-backpack company, some years after it was founded in 1989. Water is necessary for survival, but how do we know when we’re getting enough, ...

We all know the tip: "Drink 8 cups of water a day." But how did they pick that number? Is it the best rule to stay well, or just an easy tip that people have said over and over for years? The real ...