I have the Lowes branded version of the everspring. It is crazy sensitive! Probably would have the same evaporative problem.
Instead of going the water sensor route. I would put in an Aeon Multi and detect for humidity and motion together. When motion stops for X minutes and humidity is still high, then do yada yada. You could even keep the hue bulbs a sky blue or green while its still humid in the room. You could add exhaust fan control to the bathroom via this method too.
Here is my code for humidity on the Aeon