You need to factor in what keeps your body hydrated before breaking a sweat. If you've heard the term "Electrolytes", it is simply a blood mineral made up of sodium, potassium, chloride, etc. In order to be replenished before and after cardio activity, your body needs to have high enough levels so that it can function. For instance, if I'm breaking a sweat, I'm loosing electrolytes that need to be replaced via water or sports drinks. I usually stick with water while lifting and sports drinks/water for activities such as basketball or football.
You may also be interested in Pedialyte in extreme situations to prevent cramping and sustain higher levels of electrolytes than normal (marathons).