When i went on my trip in Europe, we cycled 60 - 100 miles a day on average. It didnt help i was there during that huge heatwave they had a year or two ago, but i found that during the course of a day i would go through 2 waterbottles and all of my camelback (forget what size it was) and would still end up going through another 2 waterbottles (and a bottle of gatorade when we stopped for lunch). Could also have been because of the pace we went - had to wait for the slower riders and all, combined with being out in the sun all day. Had a great bikers tan by the time i got back