This pack has ample areas to carry hydration bladders or bottles. There is a larger opening close to the back which can hold a large bladder. In addition there is a smaller pouch with a Velcro flap that can be used for smaller bladders. Other items can be carried in this pocket if one doesn’t wish to use it for water. Since I am not a fan of drinking through tubes, I carried Nalgene bottles in the two expandable side pockets. There is also a bi-directional zipper near the top flap that a drinking tube may be routed through if you carry larger bladders like a 100 ounce version and the tube can be run through either end of the flap. It can also be used for longer items that protrude like radio antennas. Like I stated before, it’s all about versatility!