Position of the water pipe unknown

It is also not to be ruled out that at least the one guy you met allowed a joke, like Siemens Lufthaken. That no wiring plan exists does not surprise me, as in my opinion there is also no connection up to your property. That would at least be the standard I would expect. The fact that it was different with the wastewater is no proof that it is the same with the drinking water. There are quite different regulations.

We have also bought an infill plot (Neubaugebiet 90er Jahre). The sewer is located on the property, drinking water and electricity are in the street. This is also shown in the sewer, electricity, and water pipeline plans. A house connection for water and electricity still needs to be established.

Unfortunately, it was unsuccessful, although I dug about 80 cm wide and up to 180/190 m deep.

As I said, I’m happy to do more search excavations, but it always takes a lot of time, effort, and sweat, and we don’t live on site.

I filled the hole again afterwards because sand/soil was already crumbling from the edges.

Did you dig the holes with a shovel? Isn’t it a bit dangerous at that width and depth? I hope you don’t have to be searched for yourself after the next hole if the ground gives way.

My actual question to the community was not whether there is a pipe there or something else, but whether a water association can evade responsibility here by clarifying obviously missing or incomplete pipe maps. I also believe that this behavior is shamelessly brazen, but nowadays you often only get anywhere with authorities / agencies by presenting facts and legal grounds.

Then I will give you an answer. A few weeks ago, I was voluntarily elected chairman of the local water supply association and am currently working my way into the issue from a "different" perspective. Our water association has statutes that clearly define responsibility for the pipes. In our case, the association is responsible up to the valve, and from the valve onward, the responsibility lies with the property owner. This does have disadvantages when searching for a pipe or if a pipe on the property is leaking, but here in rural areas it has quite a few advantages if the property owners have long pipe routes to the house. It is therefore quite possible that the association has no precise knowledge of the pipes on the property and is not required to have such knowledge. A look at the statutes or the service directory will inform you whether you are being left out in the cold or if you are looking for responsibility in the wrong place.
Solution approach:
A pragmatic approach is to talk to the neighbors, especially those who may have witnessed the construction of the house. You will be surprised how much people know as a group. On this occasion, you also get to know each other a bit and can exchange a few friendly words. This is worth its weight in gold when you start building, because if you are considered approachable, problems like a temporarily blocked road due to construction, some dirt, or other everyday minor issues do not escalate into unpleasant situations.