tried a 9 hour adventure race on the weekend (hiking/ canoeing, and biking.) Drank and ate smart... but not enough. gassed out after 7-1/2 hours. and at that point it took another 5 liters of liquids before I had my first #1 of the day.

Previous to that point, I had drunk approx 7.5 liters of water or gateraid.

What is key... is not the physical qty... the number value... but to make an honest effort to replace what you are sweating out. Strange to think that after drinking almost 2 gallons, I was still dehydrated. I should have known better, as not having to urinate is one of the first signs of dehydration.

Had this been a survival situation... I might not have...