You could use particle effects. Some samples can be found in
this thread. You would need to modify one of the osg files there to get the water effect.
We have a precipitation plug-in documented in the Vizard Help that creates rain and snow effects. It's possible that could work for your application. You won't be able to specify a certain location for the water drops as they will fall throughout the entire scene. This may not be an issue if the view is from within the shower.