Construction of a 144 sqm bungalow in Fichtenwalde (near Potsdam)

The water coming from the roof should be led away from the house and infiltrate into the ground on the property.
Normally, the downpipe is guided from the gutter to the ground surface level and then buried in an underground wastewater pipe (KG pipe). After that, there is a 90° bend, and the pipe is led away from the house into the terrain with a slope. After 3-4 or 5-6 meters depending on the size of the property, the KG pipe transitions into a drainage pipe. These are usually yellow or orange and perforated. Around the drainage pipe, there is a gravel layer made of 16/32 gravel, and around that, there is a drainage fleece. The whole thing is wrapped with the fleece and backfilled with soil. In this case, the fleece prevents the gravel layer from silting up. This is meant to ensure that the arriving water is distributed more evenly in the soil.
However, this only works up to a certain amount of water. If large masses of water come from above, the water eventually backs up and pushes the downpipes upward. Or it pushes up at the connection point between the KG pipe and the downpipe, depending on the sealing. If pine needles accumulate as well, they clog the drainage pipe and the function is lost.

We solved the infiltration quite simply. Took a green water barrel, drilled lots of holes in it, dug a hole in the ground, put in fleece (to prevent sand infiltration), coarse gravel (16/32) inside, then put the barrel in, the same gravel also inside the barrel (half full), lid on the barrel, fleece over it as well (to prevent sand infiltration from above). Connected the whole thing to the gutter and buried it so that there are still 20 to 30 cm of soil on top, and a few meters away from the house. If it really rains a lot, the water pushes out of the barrel upwards and then just runs off into the garden; nothing has ever come out of the gutter for me (and we already did it like this at the old house). That only happens during really heavy rain, and the garden is wet anyway. You could connect something like that to the cistern as an overflow if it is technically possible from the cistern side. Or you can simply make an overflow on the cistern and let the excess water drain into the garden or your forest.

Well, if the cistern has an overflow, then everything is fine. Presumably, that's why the cistern was planned over there at the back, so the water can just run off there.