A humidifier has a first sealable reservoir feeding water to a second reservoir communicating with ambient atmosphere. A blower is adapted to blow a stream of air through the humidifier to ambient atmosphere, such that the stream of air picks up water vapor from any water that may be in the second reservoir. A feeder valve feeds a quickly-evaporable quantity of water from the first reservoir into the second reservoir. The quickly-evaporable quantity of water in the second reservoir is substantially smaller than the water capacity of the first reservoir. A dry-out mechanism shuts off the feeder valve upon a user command and continues to run the blower at least until the quickly-evaporable quantity of water has evaporated to an extent effective in inhibiting the growth of microorganisms in the microorganism-vulnerable reservoir.