After having a recent dehydration hospitalization after a race, I'm nervous, so I carry water with me on all my runs over 4 miles. Which is most of them. Granted, most my weekday runs are in 100 + degrees. I just bought the book Waterlogged and can't wait to learn some more about this. I carried a small camelback at the Hottest Half marathon last August and liked having it. I did not drink any more than I think I would have with the stops for cups, but I never had to stop. I just kept on going while everyone crowded those little tables.