Originally Posted by merlinextraligh
general rule of thumb is drink a bottle an hour. Obviously varies with heat and intensity. If you can't add a second cage make sure you at least carry the big bottle. And for cages you definitely need CF
Surely that depends on the size of your bottles? If I drank one full sized bottle per hour on a group ride I think I'd do myself some serious damage. There's such a thing as overhydration.
Two large bottles should be enough for a ride up to 60 miles or so. Drink plenty before and after and you'll be fine.