I would want to test it dry....to be sure.I would think that it is thermostat controlled so water or air won't matter.
The one I have (different kind) the instructions said to put it in the freezer for a while then plug it in. The heater should come on for a couple of seconds then click off, this test is done out of water.
When I changed from the messy waterer you see in the farm stores to a nipple waterer I took the waterer out for a couple of hours then placed just the empty red bottom under the nipple. Within 5 minutes they all had it figure out. Most were pecking at the red bottom till one pecked at the shiny thing.
JT
Great nipple training tip!
Horizontal or vertical nipples?


So I'm not sure they've had an opportunity to learn from each other. But I hope that would happen!