Additional Hydrostick for the Digital Ultrasonic Humidifier. The Hydrostick provides constant freshness for your humidifier, helps maintain the appliance and improves its life expectancy. It’s good for one year and helps ensure your humidifier's functionality while providing fresh humidification performance. Its advanced water maintenance system keeps your humidifier operating at its highest level between recommended cleaning. The Hydrostick begins to function as soon as it comes in contact with water, even if the humidifier is off.