Question: We have a Honeywell whole-house humidifier attached to the duct directly above the heating element/electronics of our furnace. A few possible pertinent facts:

* The water intake is attached via a saddle valve.
* The drainage line leads to a pump. The intake for the pump is a PVC pipe, which the drainage line rests inside. The drainage line for the pump resides in a sink in another room.
* The humidistat is attached to the intake duct.

Whenever we run the humidifier, we end up with a small amount of water on the floor. It doesn't tend to appear for some time, but it consistently appears within 4-8 hours. I have never actually observed the water exiting the humidifier, so I don't know where it's coming from precisely. Part of my concern (and the reason that we don't currently use the humidifier) is that the water is draining down the interior of the duct.

I'm reasonably certain that the pump is not the reason for the leak. I've poured water directly into the pump's intake pipe and it proved capable of handling the water as fast as I supplied it.

I've also changed the filter in the humidifier, but the leak persisted.

The final wrinkle is that we had a plumber in for an unrelated issue who observed that the water pressure in our house is abnormally high (I believe he said it was 150 PSI, but I may remember incorrectly).

My questions:

1. What are the likely reasons for the leak?
2. How can I definitively determine where the leak is originating from without watching the humidifier for hours?
3. Is the high water pressure a possible culprit?

Answer: 
I can only provide anecdotal answers to questions 2 & 3.

2. I have successfully used a few drops of concentrated food coloring, at different places I suspect for leaks in a water softener and its related valves and plumbing. I used 3 different colors if memory serves me right. We had a very slow/unnoticeable leak, apart from the puddle of course. I was able to determine which valve is was based on the color dye that showed up in the leak (blue in this case).
3. The failed water softener in this case did fail due to high water pressure. I would see if there is any manufacturers rating for the humidifier's working water pressure. There is no telling what parts, valves or plumbing inside the unit make be deforming/failing under such high pressure.

Good luck in your troubleshooting and fix.
Our humidifier leaks in a similar manner, but the only way I could figure it out was to run the humidifier and watch for it (sounds awfully boring). I tracked it down to a tiny leak in the spout that feeds the overflow tube. The drops were running down the tube and leaking off the lowest point (where it curves), which was a few inches away from the humidifier. Good luck!