Info from Manufacturer: Our newest humidifier is designed especially for your ukulele with two unique features: A mounting system that allows the humidifier to hang horizontally inside the ukulele rather than vertical (like the guitar humidifier). A humidity output of about 50% of the blue Oasis guitar humidifier, to accommodate the ukulele?s smaller instrument size. This also allows the humidifier to last twice as long between refills. The exclusive Oasis® design of all our humidifiers makes the Oasis® Ukulele Humidifier easy to see when to refill, provides long-lasting humidification, ensures no leakage due to overfilling, and promises two levels of leak protection. Because tap and bottled water have dissolved minerals that can clog the liner, distilled water is recommended to extend the useful life of your ukulele humidifier.