If you're still holding onto the notion that eight cups of water a day is sufficient (I bet you also still believe that you need to wait 30 minutes after eating to go for a swim), you're not working at your body's peak performance level.
"Water makes up about 60-70 percent of our body and plays a role in virtually every function, from keeping our blood flowing and skin healthy right down to our ability to blink our eyes," says Wendy Bazilian, Dr.P.H., R.D., "Water is our most important nutrient."
Sure, hydration is important to survival, but if you are healthy and have access to clean water, death by dehydration probably isn't a major fear. So why should you be concerned with hydration? Even mild dehydration can begin to compromise your health and stifle the effectiveness of your workout. And conversely, overhydration during outdoors workouts can drastically lower sodium levels in your blood, and even lead to death. Here are the top five things you need to know about water, and how much your body really needs.