A humidifier for treating humidified air with germicidal light is provided. The humidifier includes a water reservoir, an atomizer to atomize a supply of water, and an ultraviolet light source to expose the atomized water to germicidal light. The ultraviolet light source extends vertically within a cylindrical channel to irradiate the atomized water dissipating upwardly from the atomizer. The water reservoir can include a carbon filter and a hardness-removing module for removing containments and metal oxides from the water supply. A control panel indicates the remaining useful life of the ultraviolet light source, the carbon filter and the hardness-removing module based on historical humidifier usage and water quality levels.