The human body is about 50 to 70 percent water, and it needs pretty much all of it.2 You’re constantly losing water, not just from sweat but also from urine and more subtle leaks like the moisture in your breath. And, under normal circumstances, you’re constantly replacing it by eating and drinking. Your fluid balance fluctuates a bit throughout the day thanks to meal and activity patterns, but from one day to the next it’s regulated with remarkable precision.
