I don’t know a supplier directly but I would suggest you go with 30 gallons at most for potable water ... even better go with a WaterBrick system of multiple 3.5 gallon totes that are much easier to handle and can be stacked and stored in a variety of configurations to fit your space. Remember a gallon of water goes a little over 8lbs so 55 gallons is over 450lbs water only ... even 30 gallon goes about 250lbs water only. Each WaterBrick filled is about 27lbs total with its carry handle is very manageable.
I just went to a water distributor and bought full 5 gal water bottles. You can stack them with plywood and they can make shelves or tables. Not as efficient space wise as cubes though.