This invention is an improvement to the existing reverse osmosis water filtration systems used in under-the-sink and similar commercial applications. This improvement uses a thermally conductive liner that allows an increase of efficiency to heat or cool water within the reverse osmosis system. In addition, it includes a controller that determines the amount of cooling required without contact with the water. The controller provides slow-rate pulse-width modulation of the Peltier-like device to cool, and dependant on room temperature, potentially heat the water within the reverse osmosis system.