That sounds unusual. Was that warning letter about lead in the lines from the public utility ( https://www.hamburgwasser.de ), or the pipes internal to the house?
No, it is now nine years ago, but I think it was from some state government agency. I know it was not from Hamburg Wasser, as it concerned not the public lines, but from the house itself. And I just saw that beginning next year it will be not allowed anymore: https://www.hamburg.de/politik-und-verwaltung/behoerden/bjv/...