You're probably already dehydrated. Not severely. Not enough to land you in the emergency room. Just enough that your body may be working a little harder than it needs to. Most people think dehydration starts when they feel thirsty. In reality, your body starts responding to changes in hydration before you necessarily notice it. Those changes can affect a lot more than your mouth. Your energy. Your concentration. Your mood. Your exercise performance. Your kidneys. Your blood