Can a water drop do a "fake" touch on a capacitive touchscreen?
Capacitive sensors react to the polarization of a conductor or dielectric that touches (or is close enough to) its surface, so the size or connection to the water should be taken into account. An isolated drop might not affect it, while a stream of water will. I have a large trackpad for my computer, and an app that visualizes its input. I put a fairly large drop onto the trackpad, and it wasn't registered. When I touched the drop, it opened a path for the electric field into my body and that activated the sensor and registered, etc. 

So what I'm saying is that drops of water on a touch surface won't affect it by themselves, though your results might vary depending on the implementation. Still, water on the surface might mess things up since it could make streams, or connect with someone's finger and cause jitter. Hope that helps.