Reverse osmosis filtration systems that are self contained and easily converted from above the counter use to below the counter use. The systems feature a simple construction, including a two piece manifold assembly to which filters, including a reverse osmosis filter, a product water storage tank and a control valve connect, all without separate fasteners. The manifold assembly provides all water connections within the system, and includes connections to connect to a water supply, a drain, two dispensers and to an auxiliary water storage tank. The system pressurizes squeeze water for product water dispensing, providing maximum efficiency, maximum storage capacity for a given tank size and maximum pressure for dispensing product water. Various embodiments are disclosed.