Go with the camelback. Then you can go far, far away from convenience stores and fountains if you want. And fill it up. The one time I half-filled it—for what I thought was going to be a shorter ride—I drank it dry in about three hours. I was ready to try sucking water out of mouthfuls of gravel by the time I came off the mountain.
It makes my back sweaty, but I'm not all that alluring when I get off the mountain, anyway.