I just got my new electric Bosch boiler because my old one has been making strange noises, now im a little bit scared.. can i get electrocuted trough water while im showering..should i turn it off while showering and how smart is that.. :D
If it has been properly installed, you cannot be electrocuted. The metal parts of the boiler and any metal pipes will be connected to earth. If there is a fault, your breaker will disconnect the electricity. If you are concerned check that the electric circuit that powers the boiler has RCD protection.
There are several defenses to an electric shower water heater hurting you.
First is the house's earthing system, the neutral-ground equipotential bonding in the service panel, and the the earth wires up to the water heater. If the heater is largely steel, it means all of its guts (except for the heating elements) are grounded, and any leakage current will be whisked back via the green/bare grounding wire, back to the panel, where it will be returned safely to source. If the current is excessive, it will trip the overcurrent (breaker) protection.
Second is a special module your panel may have, called an RCD (Residual Current Detector) aka (American) Ground Fault Circuit Interruptor. This module compares the current on the hot wire versus the neutral wire. They should be equal. If they are not equal, some current is going the wrong way! e.g. through you, and in that case, the device will trip. It's a superb system and some say it works even better than grounding. It is allowed as a substitute for grounding in cases whre grounding is difficult to retrofit.
Now your house may have this protection. You have to look in your panel for an RCD. Normal practice in European homes is to have a 30ma RCD protecting the whole house, and the goal is to protect the house wiring from a variety of faults. Normal practice in America is to use 8ma RCDs to protect each individual circuit, and the goal is life safety. Why a difference?
When life safety is the goal, an 8ma RCD is better. Electric shocks in the 8-30ma range will be missed by a 30ma RCD, and can pack a heck of a wallop. They are unlikely to kill, but certainly can stun -- and a stun is a kill if the direct result is a drowning or bad fall.
So in Germany, your typical situation will be a 30ma whole house RCD. Your ideal situation is also an 8ma RCD on the dedicated shower water heater circuit. And a ground/earth wire from the RCD to the service panel to the neutral-ground equipotential bond.
Nobody puts 8ma RCDs on the whole house, because a fair number of appliances leak a tiny amount, and a house full of them has a fair chance of exceeding 8ma sometimes.
Now what about water pipes as grounding path? #1 that breaks if someone replaces a section of metal pipe with plastic, and how do you know they haven't already? #2 water pipes are simply not made for that. If they were, there'd be a stack of additional rules about how to sustain pipe's current-return abilities. Not least because ... #3 galvanic corrosion really is a thing. It won't matter until current leakage starts, but when it does, it will dramatically accelerate pipe corrosion. Just ask water companies what happened to water and sewer mains parallel to trolley tracks.