Our rental agreement (Germany) actually contains instructions on how to ensure that a certain kind of bacteria (legionella) doesn’t build up in the apartments p

Our rental agreement (Germany) actually contains instructions on how to ensure that a certain kind of bacteria (legionella) doesn’t build up in the apartments plumbing. If you are gone for > 7 days, open your taps on the hottest setting and let them run for 2 or 3 minutes. Let them run for a minute on the cold setting. If you have a house rather than an apartment, maybe check whether there is any filtering system installed that would need a potential replacement.