Electric shocks of vibration off shower?

I had a new bathroom (wet room) installed few years ago. I have noticed that occasionally it feels like I am getting electric shocks off the shower tap. Initially I thought it was vibration as when I press on the shower tap, it seems to stop. But my flat mate says he is getting shocks when he touches the shower head (waterfall shower head into wall) and the shower tap to switch off the water. It doesn't happen every time the shower is used though. Do I need to call a plumber or electrician or is there a specific bathroom specialist I need?