Rainwater must be obligatorily infiltrated

The house is about 9x10m without the extension. So not huge, but not very small either.

I already suspected that, but it really looks like a Smurf house next to the huge cistern! :D

Definitely find out. Ask the neighbors or have the soil survey done earlier. If the cistern is unstable, I would definitely not wait until the end to address the question of the white bathtub.

Hmm, we were always told that you only do the soil survey once you are 100% sure where the house will be. Now that I say it again, it occurs to me that I can't believe the house would be moved after submitting the building application :confused:. So I'll start looking for a soil surveyor... Thanks for the warning!

Either you have a building plot that is relatively even. Then it doesn't matter if you move the house by 3 meters or make it 1 meter wider. In that case, you can also carry out the soil survey in good time. Or you have a building plot where every meter is completely different. Then, despite drilling at the corners, you still have surprises when the excavation pit is dug ;)

We have to submit a "wastewater technical calculation," I'm very curious how he will do it...

Normally it takes 3 hours for the architect. All sealed surfaces are added up, from that the amount of precipitation to be discharged is calculated, and accordingly the size of the soakaway is dimensioned. This is then marked on the property (e.g., in the garden) and submitted as a plan with the calculated values.

By the way: Some use/calculate with bucket soakaways (expensive), others with common pipe soakaways (cheaper).
At the time, we planned with bucket soakaways, shortly before implementation it turned out that these would be significantly more expensive and were not available. So we switched to cheaper pipe soakaways and even commissioned another architect who recalculated it for 200 EUR. Then off to the office..., although this is only a "formal act" and no one really cares about the details in the end.

What does that mean? A meter for garden water?

Depending on the municipality, you can simply install or register a water meter on the outdoor faucet (for garden use) and in the end pay no wastewater fees for the amount of water used. Some have one sealed by the water supplier; in others, you can simply "register" your own meter and that's it. These cost a small amount of money and pay off quite quickly since the costs without the wastewater portion are significantly lower for consumption.

That would be extremely cheap! For a deep well pump? Or just a suction hose?

"Just a suction hose," I assume :)

We have buried a plastic cistern here. It cost 750 euros a few years ago.

Hole and everything else was done by ourselves.

A soakaway was not an option.

[*]I didn’t feel like spending 100 euros on asking whether something like that is allowed to be installed.

[*]The question was whether after a few years a lot of dirt would accumulate inside so that the soakaway would no longer work properly.

[*]I would have had to fight with roots from trees and bushes to be able to bury this soakaway.

So I took the simplest solution. From a certain water level, excess water is pumped into the garden where it can then seep away on the surface.

Regarding the size. There are various sites where you can calculate the cistern size. Unfortunately, they sometimes come to different cistern volumes with the same initial values.

I would not use concrete shaft rings. They are quite heavy even with small diameters. And thus probably only transportable and installable with special clamps. In addition, a digger or something similar might be required to install them.

Well, an excavator should probably be the least of the problems when it comes to the groundwork. You use it to install the rings as well.