Why do you pee when you hear the sound of running water? Watch the video, where you will find an explanation of this phenomenon.
What's wrong with peeing you when you hear the sound of running water, should it be the one from the tap, waterfall or rain?
As you can see and hear in the video, they are for faking the need to urinate blame our brains. It is a conditioned reflex, as the sound of running water is very similar to that of peeing.