Is the Legionella bacteria multiplying in plumbing? What is the risk of getting it if I drink water from a tap, maybe it is safer to use bottled water from a bottle?

Legionnaires' disease cannot be get sick by drinking tap water! Yes, bacteria can end up in plumbing there to live and multiply, but the danger can only arise if it enters a humans lungs, not the stomach. This can happen at a certain temperature, above +40 degrees of Celsius, when the water evaporates. So the risk of getting sick is by inhaling bacteria, taking a shower, ventilating and conditioning systems, not drinking water. From a safety point of view, it doesn't matter if you drink water from a bottle or tap! However, to reduce the risk of "catching" dangerous bacteria when taking a bath, drain the water at maximum temperature for at least 2 minutes before use!