Master showerhead has electrical current, what to do?
This is how some of our troops got killed overseas. Simply taking a shower delivered lethal doses of electricity.

The problem is grounding.  It is certainly possible that the ground in the breaker box has become separated from a real earth ground.

So first, the breaker box ground needs to be fixed at the very least.
Even if it requires driving in a new ground rod and new wiring.  Then make sure all ground connections are tight.  

Highly recommend a qualified electrician to look at this one.