Is there a water bladder sleeve that fits?...
Is there a water bladder sleeve that fits? is it functional?
Yes, and yes. There is a pocket that holds the removable frame panel and holds a hydration bladder. I have 3 liter bladders from both geigerrig and camelback. They both fit fine with or without the frame back panel. There is a tube slot from the top that allows tube access from both shoulders and the hydration pocket has a bar that can clip the top of the bladder for increased bladder stability. I've also seen the bladder placed in the front stretch pocket for easier access, though not as efficient when hiking.