Jim, I just tried a couple of options with the water bottles. The small sack that the Ribz ships with holds a 1 LT Nalgene bottle with a little room to spare. On the sack, there is a small ring that a carbiner can fit through and I attached this to the left back strap. I found that the weight of the bottle pulled the Ribz down on a angle that made it a bit uncomfortable to wear. I adjusted the straps some so that Ribz rode a little lower and helped a bit but still an idea setup.

Next I tried a 750 ML bottle in a small sleeve I already have and attached in the same manner as the above. This was much better due to the lighter weight of the bottle but still not to my liking.

Next option is to attach the bottle sleeve just to the outer side of the small front, zippered outer pocket. This may just center the weight of the water and bottle so that it does not pull down on an angle towards the back as much. This will have to wait until tomorrow as it is time to go swim some lengths at the pool.