Why You Might Be Dangerously Dehydrated

When you skimp on fluids (check out the ideal amount here), it’s hard on your body, which makes sense because water is essential to just about every process in our body and, in fact, to the very existence of life on Earth. Life first emerged in the salty, primordial ocean; it stayed there until it was able to capture a bit of that water inside itself, the so-called “milieu intérieur” in which cells are bathed. Our inner ocean is a calm, salty broth providing cells with the raw materials they need to function, removing waste products, allowing them to communicate with each other and buffering them from the unpredictable world outside.

This water within accounts for about 60 percent of our body — about 11 gallons, or 92 pounds, inside a 155-pound person. Most of it lurks inside our cells (where all sorts of important substances are dissolved in water) and outside them (the milieu interieur), but we also use it to cool our body with sweat, to circulate oxygen and fuel to our organs and to take away waste products via blood. The elderly, infants and sick children are most prone to dehydration, but no one is risk-free. “lf you’re really busy, it’s easy for all morning to go by and you don’t really drink much until you notice you are thirsty, at which point you’re already slightly dehydrated,” says Cheuvront. And when we exercise hard, such as playing soccer or football or running distances in the summer, and forget to hydrate, we can easily lose 4 to 5 percent of our body weight (take a look at the best after-workout drinks here).