After you exercise, your goal is to fully replace any fluid and electrolyte deficit. How aggressively you rehydrate depends on how quickly you need to recover before your next exercise session and how big a fluid-electrolyte deficit you incurred. Most active people can recover with normal meals (that contain a little sodium) and plain water. If you are significantly dehydrated and need to exercise again within 12 hours, then you need to be more aggressive with your rehydration program and sprinkle extra salt on your food if you had high sodium losses through sweat.
Drinking 50 percent more fluid than you lost in sweat will enhance rapid and complete recovery from dehydration. (The extra fluid accounts for what gets lost via urine.) Sipping fluids over time maximizes fluid retention and is preferable to drinking large amounts in one sitting. If you become dehydrated during an unusually long and strenuous bout of exercise, you should drink frequently for the next day or two. Your body may need 24 to 48 hours to replace the sweat losses.
If you become more than 7 percent dehydrated (either by sweat losses, diarrhea, or vomiting), you will likely end up requiring intravenous fluid replacement under a doctor’s care. In most cases, there is no advantage to taking fluids by IV, unless for medical necessity. Your best bet is to stay out of the medical tent in the first place by knowing your sweat rate and drinking accordingly.