It's a remnant from my old days as a nordic skier back in NH. When we would go on 3-4 hour overdistance skis out in the woods, or 2 hour long runs in the summer, we would have to bring water with us. No Camelbaks in those days, so we all had water bottle belts. I still have a few of mine leftover from my HS/college days, so this year I decided to start bringin it to pracitce.
Yesterday, my old water bottle belt saved my bacon. I was having a tough day, but by being able to take small sips of water throughout my run, I made it through 2.5 laps of the XC course. I was pretty tired at the end, but I was able to get in a safe, efficient productive workout, even though I was having a not-so-great day.
If you want to get one, any specialty running store (Boulder Running Co. Runner's Roost) or even outdoor stores, (REI, Wilderness Exchange) will have them. They are great to have, just don't use them when racing!