Air-O-Swiss AOS 7017 Hydrostick This advanced water maintenance system keeps your humidifier operating at its highest level between recommended cleanings Good for one year, the Hydro Stick ensures your humidifier's functionality while providing fresh humidification performance. The Hydro Stick begins to function as soon as it comes into contact with water, even if the humidifier is switched off. Using the Hydro Stick helps to maintain the appliance and improve the life expectancy of the humidifier. Exchange the Hydro Stick a year after it has first been used.