A reverse osmosis product water storage tank having first and second molded shells coupled together to form an enclosure, a bladder within the enclosure and coupled to separate product water from squeeze water within the enclosure, a first port through a wall of the enclosure to provide water access to the product water side of the bladder, a second port through a wall of the enclosure to provide squeeze water access to the squeeze water side of the bladder and wherein the inner surfaces of the enclosure having a topography configured to define a plurality of channels between the inner surfaces of the enclosure and the bladder when the bladder is full of product water for accommodating squeeze water flow into the enclosure between the enclosure and the bladder when the bladder is full of product water.