A specially treated filter cassette absorbs the water from the water tank. Fans move dry air through these soaked filter cassettes and blow the humidified air back into the room. The humidification is not visually visible. A great advantage of an evaporator system is that over-humidification is not possible. Saturated air will not continue to absorb moisture with this system and so the output is automatically regulated. Further, evaporator humidifiers require very little power and work extremely efficiently.