The Everlasting Comfort Ultrasonic Humidifier is designed not only to serve its true purpose as a full room humidifier, but it also functions as an oil diffuser with a dedicated aroma tray. Unlike any humidifier on the market, this is a combination of a large capacity 5L humidifier and an oil diffuser. Simply add your favorite essential oils to the tray, fill the tank with water, and head into deep relaxation. IMPORTANT NOTE When re-filling the water tank, remove water tank from base and cover the bottom of the water tank with a towel to avoid condensation from dripping on the floor.