Bought a $15 water bladder with hose/mouth piece from Amazon. Dark green color. Set the water bladder in the back "bird carrier" part of vest and run tube up and over left shoulder and down the strap. Hold it in place with three black zip ties around the strap cut down to size. From messing around with the fit is should work perfect. No more crinkly water bottles in my pack making noise as I try to get in tight to a bird in the dark etc.
Any of you all ever added a water bladder?