That is lot of water in a short amount of time. As you urinate that much water or sweat it out, you will be losing lot of electrolytes and minerals from your body, which can deplete sodium, potassium, magnesium and zinc. Too much loss can cause your muscles to cramp and even irregular heartbeats. This is the very reason why we do not give straight water in IV's. They are always with sodium , which is what we call normal saline, and we often add a little of potassium in the IV bags when we hydrate our patients in the hospital. I would consider half in water and half in coconut water, which has all of these electrolytes and minerals. If you don't like coconut water, you can always replace with Gatorade.