Shocked while showering : How is this electricity getting into the hose system ? I live in a underground room level [private] apartment. There's a waddle in...

I live in a underground room level [private] apartment.
There's a waddle in shower and when the metal plate astern the water knob is touched, I acquire a (low) shock ; this is especially noticeable if at hand is maybe a rake up on my hand.
I get my Multimeter and set it to the 200VAC scale and touched one organize to the plate on the wall and the other lead to the damp tile floor and/or even the metal drain cover and I was getting a reading of 2.5 volts AC !
How can I trace this to find it myself and prove it? The hotelier won't find or fix it ? I want to go to the township to carry a resolution !

Need any more details just ask I will update this !
Answers:    THIS IS DANGEROUS HAVE IT CHECKED!!! That said...
Sounds close to you plumbing system lost the ground. There should be a ground rod driven into the ground which is wires to the Ground/Neutral bus bar contained by the electric panel. The cold water pipes within the building should also be wired to this same Ground bus bar. If the telecommunication to the ground rod gets broken, conceivably by a lawnmower or something then the plumbing ends up near a small voltage on it from the Neutral bus bar which is no longer tied (referenced) to ground. Since the floor of the shower is sort of connected to ground through the drain the electricity go through you from the plumbing to ground. Another possibility is someone added a sub-panel without a separate (from the neutral) Ground bus block. Either way it's a ground problem. See suggestion below.
Yes, go to the township. This can be risky! Maybe before building that shower surrounded by the basement... near was some sort of outlet in that and didn't cap it rotten when installing the shower. Ya know, water and electricity don't mix. Please go and get it checked out!!