what did you use to rehydrate? Just using a LOT of water is a bad idea (unless you eat a good amount, with salt and other nutrients around that time). Because as we all know, this can lead to hyponatremia (at the risk of stating the obvious: you sweat out a lot of salt with the water you lose. Only replacing the water dilutes your blood (serum). Water moves from the extracellular fluid to inside the cells to balance the concentration on each side. This can lead to swelling of brain cells). Also, large amount of water taken at once will often be peed out fairly quickly, therefore causing you not hydrate very well.
As others mentioned, you need electrolytes to better absorb and maintain fluid. Adding carbs and proteins further enables one to maintain fluid better than just taking in water (due partly to slower gastric emptying). Milk has all of these. Milk is actually the best hydration drink you can consume. but of course, some combination of plain water, milk, juice, gatorade, and food will do the trick, and not only rehydrate you, but aid in glycogen resynthesis and protein rebuilding.
In response to the OP, first, see what I wrote above, and second, one needs to take in more water than they sweated out during a workout in order to rehydrate due to urine loses and further sweating post workout.