About the Aprilaire 4407 humidifier water distribution Tray for Aprilaire 400 series humidifiers the Aprilaire 4407 humidifier water distribution Tray is a Replacement part for Aprilaire 400 series humidifiers. The Aprilaire 4407 humidifier water distribution Tray distributes the water evenly across all portions of the evaporate panel by simply attaching to the unshaped scale control insert and incorporating a pumice coating inside.