It is very easy to gain and lose water weight quickly if you are in top shape. In college I lost 13 pounds in 8 hours and put it back on in 1 hour. Not a recommended practice. We found out we could weigh-in a day early because the team we dueled wanted one weigh-in. They had a meet the night before us. Both coaches agreed and the rest is history. It took three different workouts to get the weight off. It only took one sitting or standing to put it back on.