Air-O-Swiss E2441 Evaporator Humidifier The Hydro Stick (included - replace once per year) keeps the humidifier clean and fresh longer. This advanced water maintenance system keeps your humidifier operating at its highest level between recommended cleanings. It is self-regulating and maintenance-free. Included lifecycle replacement indicator lets you know when to change the Hydro Stick. No White dust - The evaporative method of humidification is the most natural and healthiest way to add pure moisture to the air, without leaving any white dust or residue from mineral deposits. Replaceable wick filter traps any impurities or minerals that are present in the water Top fill design - simply pour water directly into top of unit. No heavy water bottles to carry or fill Easy handling and cleaning - unit can be taken apart in just 3 steps Visible water level thanks to a floater that indicates when the water base is full