There are a couple of threads on hydration if you do a search. To me, a handheld really interfered with my arm swing. I used a 3-bottle waist pack for a while (the single bottle one was HORRIBLE, bounced and sloshed all over the place besides really inhibiting hip rotation), but a full 60 oz of water in my Nathan Intensity pack weighs me down less than 24 oz in the waist pack. Love the thing, and it's got plenty of room for whatever else you need.