Take the guesswork out of rehydration. Learn your sweat rate by weighing yourself naked before and after you exercise. A pound lost after exercise equates to losing 16 ounces of sweat which means you should drink 16 ounces of fluid to rehydrate the body. Throughout the summer months, you may notice a greater loss. Always drink plenty of water and on the longer runs, make sure you are brining water with you in a hydration belt or pack.