A heat sanitization system for a reverse osmosis system that utilizes the pure water produced by a reverse osmosis unit to sanitize the various conduits and components of the reverse osmosis system. The pure water from the reverse osmosis unit is collected in a storage tank during a tank fill cycle and, during one of the sanitization cycles, that pure water is withdrawn from the storage tank, heated to a desired sanitizing temperature and the heated, pure water is circulated through a selected flow path of the reverse osmosis system for a sufficient period of time to carry out sanitization. A control system allows the user to select the particular flow path for the sanitization cycle or the flow path can be automatically determined by the control system. There are also cool down cycles that selectively cool the particular flow path after a sanitization cycle.