Voltage between shower faucet and drain
No, this is not normal and dangerous. I suggest that you hire an electrician or least favorable option (ground is like crazy science to regular person and there are a lot of gotcha ya), do your own research. It looks like there is insufficient grounding and your heater or some other appliance has a ground fault. All of the electrical circuits and appliances must be grounded and all metallic piping must be bonded.