In order to provide for their passengers comfort, SwissAir brews up fresh coffee and tea in their passenger aircrafts and in a jumbo jet up to 20 coffee machines and hot water boilers are installed for this purpose. The water used often contains minerals depending on the location of the airport. For reasons of space and weight a decalcifying installation is out of the question and the taste of the coffee or tea would also suffer from this water treatment. For this reason the coffee machines and boilers are decalcified at regular intervals at the aircraft hangars of the home airport. The following neutralization and passivation processes remove the residues of the decalcifying agents and protect the installation.