This article is from the Misc Bicycles FAQs, by various authors.
Drinking before a race or ride is just as important as drinking
during the ride. Just drink a large glass of water or juice
(unsweetened, of course) and, if you drink coffee or tea with
breakfast, another glass to counteract caffeine's strong dehydrating
After a long ride many cyclists notice a significant weight loss.
Ninety-five% of this lost weight is water. To recover quickly replace
the lost fluid by drinking two cups of water every half hour for every
pound lost. Do not rely on your sense of thirst. Delaying the
rehydration will also delay recovery.