If there were dissimilar metals in contact with the water for a long enough time, then corrosion/rust could be a problem, even if the device was never powered up while it was wet. But, the prognosis is good, if exposure was short.
After the "Northridge Earthquake of 1994", a fire sprinkler pipe broke in the warehouse at the company I was working at, at the time, and water sprayed over a large portion of the circuit board inventory. We spent the day using compressed air to blow water off the boards and then we used the parking lot to lay them all out under the sun on tarps. It was winter, but it was also a relatively warm day, as can happen in S. Calif.
It worked. All but a few of the boards (damaged by falling from the shelves), were recovered. We retested each one, applying power and running them through the standard test procedure.
In that case, the exposure was relatively brief, and power was never applied while the boards were wet. Applying power to wet electronics, will surely cause damage due to excessive currents and electrolysis. So, make sure the humidifier electronics are truly dry before applying power. Water will wick into spaces between parts and between the part and a circuit board, or anywhere there are places where capillary action will be induced. It will take longer for this water to evaporate, so make sure to give it enough time. If there is no sun where you are, then carefully use a hairdryer, making sure to not get the board or components too hot--use it on the electronics, like you would on your own hair, with the goal of getting all of the electronics evenly warm (around 120°F) for an hour or two.
Check these out for other ideas:
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http://www.theblaze.com/stories/2012/12/07/ce...can-dry-your-water-logged-electronic-devices/*
http://www.apartmenttherapy.com/how-to-dry-out-and-hopefully-s-107945BTW: Don't use WD40 (in case you possess the arcane knowledge that the "WD" in WD40 stands for "Water Displacement"). It will harm certain kinds of plastic that might be present within or around the electronics.
