German DIN 1988 prescribes a DVGW-tested protective filter, regardless of the pipe material. However, complete protection is only given if the protective filter has already been installed before the drinking water installation is filled for the first time.
New, bare metal pipelines are particularly susceptible to pitting corrosion. In addition, it is precisely when commissioning a new drinking water installation that the risk of dirt particles being washed in is greatest.
If the protective filter is retrofitted, particles may already have been flushed in. However, by installing the protective filter, you can prevent further dirt from entering the installation. So it is never too late for a high-quality protective filter.