You can use the UV sterilization function before using your LIZ, to make sure it's fresh and ready for you. Please note that the sterilization process does not extend to the bottle's rim nor the outer surface of the bottle, so you should clean these parts before use. As for the bottle, if you only use it for water, rinsing it should be enough.However, if you use it with other beverages (tainted or sweetened ones for instance), you will need to clean the bottle to remove the stains and deposits.