You can check how much you need to drink. Go "Fluid Calculator. I usually drink a lot before the practice/race and also drink as I run.

http://www.gssiweb.com/tackleheat/index.cfm

A stiff drink prior to any run is not good. All kidding aside, keep in mind you don't want to fill up on fluids too much in the minutes before running, all that sloshing around in your gut is not good. Stay hydrated in the days up to a long run, then supplement while running. Generally I will not drink during runs 7 miles or less. Although keep the weather and your sweat rate in mind as well.

I think it depends on your current training habits. My wife and I hydrate ALOT compared to most. I am an oddity because I can go run right after eating a large meal or drinking alot of something without it upsetting my stomach or causing cramping. Granted if you are out for ultimate time and performance you don't want your body requiring blood to your stomach for digestion and stealing it from your muscles. But if you are out for enjoying a run, doing a marathon for completion rather than competition, then do whatever you want and works for you. I can really tell when I go for a run and have not had enough hydrration......so I always drink.
Ran the San Antonio marathon Sunday and this is what I did. .... Saturday the day before, drank 6 24ounce bottles of water, then the morning of chugged a 24oz bottle an hour before the race and sipped another until the start. Stopped at every water station, ate Cliff shot blocks (1 pkg) every hour during the race and had a kashi bar an hour before the race.
Granted....I had to stop 4 times to use the bathroom during the race, but I wasn't trying to win the thing and I sure as heck would prefer adding about 5 minutes to my total race time (for bathroom breaks) than finish a 1/2 hour later or not finish at all because of dehydration.
Just listen to your body....folks require different things, so much of it is mental, so get it sorted out before a race. Find something that make you feel strong even after you finish and do it. In hot weather.....always err on the "more" side. We trained through 100+ degree weather and did fine except for one run (12 miler) the wife didn't hydrate and nearly collapsed. Better safe than sorry.

well i run the 5k 8k and 10k during cross country season and i usually pollish off about 4-5 ounces of gatorade lemon lime endurance formula about 40 minutes before race and it works wonders for me clocking a 16:12

I do train w/ H2O & GA but not until I get into high miles (10 plus) Then again I live in the deep South so if it's really hot I put frozen H2O bottles at every 3 miles no matter the distance. The week before a full or 1/2 I have a routine of one "real" GA a day (not a powder mix but a bottle from the market) and I up my regular water in take a little. Then, four days before I salt my food a little more. Once race day arrives, I get nervous, then check my watch fifty times to make sure I am on the right time zone as the race (if I am traveling) drink one btl H20 one real GA and pop a GU after the start at mile 1.
Like said before, it is very important to not over hydrate. It is also key to train with whatever you are going to use during your race. If you don't GU or gel then don't decide to try it on race day..it could be ugly. Just my 2cents...
Happy running!!

32 bucks a bottle? How ever did they complete marathons prior to this product? The ancient Greeks ran with nothing but water. Get a grip! This stuff better knock 1 hour off your marathon time. Then take you out for dinner afterwords. Buyer beware.