That is no wonder, because the Germans seem to be extremist with this. We have had similar problems in Finland: my local water utility had to flush some clean water straight to the sewage system, because people started saving water and sewage lines started to clog up.
You can get around this problem partially by designing the sewage system to deal with this (handles better a larger portion of solid matter in the wastewater, includes pipelines for flushing fresh water through it).
Still, too much frugality is not a good thing. We nowadays use washing machines and dishwashers that are built to German specification.
The washing program is a compromise of water amount, temperature, duration, and mechanical wear during the wash. We now have machines where the water amount and temperature are prioritized. Thus the washing program takes a long time, and it puts a lot of mechanical wear to clothes.
This is OK for Germany, where water is somewhat scarce. You have one city pulling its water from the Rhine, purifying it, using it, and putting the managed wastewater back to the Rhine, then the next city a few kilometres downstream does the same, and then the next. The purification is an expensive process.
But we don't have that; we have a pipe from a lake that contains already-drinkable water in abundance, and it needs just a bit of cleansing of solid matters before delivering to consumer pipes, and it is better than in Germany. Then, after using this water, the wastewater needs to be managed, regardless of where the clean water came from
But now the bottom line is, we save water that we wouldn't need to save, then we flush sewage pipes with fresh water, and when I put my clothes to my Miele, I wait for two hours to wash the cotton program, and wear out the clothes too soon because the washing machine rubs and whirls them half-dry.