Is the offer for the dimension for infiltration justified?

PS forget the cistern, it's not worth it

Why not? We don't have one but when I see how fast the meter runs while watering, I would be glad to have such a 10m3 cistern. Especially since a soakaway pit is mandatory for us.

PS forget cistern, not worth it

Such general answers are not helpful without justification.

Just ask directly at, for example, the company Graf. I bought the stuff from them and they calculated the size of the infiltration trench for free. The data they needed was already included in the soil report and the drainage plan from the architect.

Great! Although I have visited their website several times, I completely overlooked that. I will inquire there directly! Thank you very much.

Regarding the topic of cistern or not, I would also be interested to know why one should not install a cistern. Even if the water might run off quickly, you save quite a bit, right?

You can calculate a cistern in isolation as an investment and find that the ROI is long. Now you have opportunity costs, since the alternative to the cistern is not "no expense." That certainly results in a very different calculation. Additionally, the use of rainwater for the garden is also ecologically sensible. An alternative would be a private well.

General answers without explanation are not conclusive.

Anyone who masters basic arithmetic can explain it to themselves. The discussion has already taken place here dozens of times.