One or more preventative maintenance mode parameters for an inkjet-printing device having an inkjet-printing mechanism are determined based on a water loss rate of water from ink within the device and/or on an air gain rate of air into the ink within the device. As such, periodic performance of a non-user-initiated preventative maintenance mode based on the preventative maintenance mode parameters results in the ink within the inkjet-printing mechanism being sufficiently fresh so as not to affect quality of image formation by the inkjet-printing device. Therefore, the non-user-initiated preventative maintenance mode for the inkjet-printing device is periodically performed based on the preventative maintenance mode parameters to eject at least some of the ink from, and to refill fresh ink into, the inkjet-printing mechanism.