The invention is a hydration system that is worn on a user's arm. The system has a flexible sleeve that is conical or forms a conical sleeve that fits a person's forearm. A bladder, made of a pliable material, attaches to the sleeve, and has a number of expandable ribs. The bladder is for holding water or liquid for drinking. The bladder can be flat and folds with the sleeve to form a gently tapering form. A frame secures the bladder to the sleeve. A cap is detachably connected to an opening of the bladder, and a drinking straw allows a user to withdraw water from the bladder.