It's important to clean the Selsiuz Cooler internally annually or whenever the system hasn't been used for 15 days. Use the Selsiuz Cool cleaning kit for this. The kit contains 200 ml of cleaning fluid, a cleaning cartridge, and a funnel. Proper cleaning instructions are provided in the manual included with the 4-in-1 or 5-in-1 system. The manual can be downloaded from this website under "Installation - Installation Help."