The model V790 humidifier uses a two-step approach to eliminate potentially harmful microorganisms from the water before they are spread with the mist into the air. The first step uses a UV bulb, located inside the base of the humidifier, that shines on the water through a special glass tube as it passes from the cold water reservoirs to the hot water reservoir. The second step is the boiling action that takes place in the hot water reservoir just before the mist is distributed to the air in the room.