Yes, you know you need to drink... but don't forget the gatorade or sports drink! On event, you should be drinking approximately 1 bottle of water AND 1 bottle of gatorade every hour. I know this seems like a lot to drink but your body needs the fluid. Remember how much you sweat! You need to replace that fluid! And both are needed to help your body recover from this vigorous activity.
Plus remember to actually start hydrating for the event a couple days before the event. You should be drinking enough during the day that you have to get up at night to use the restroom.... yes, it should wake you up! ;) This is also true on event. Plan on at least one trip to the portapotty at night.
Remember ---- Drink + Pee = No IV! ;)