Basement floor - Who knows what these holes are?

So if they were really drying holes: how can you not remember something like that? That would seem strange to me, I must say. Didn't you have an expert on board when buying the house?

We bought without an expert. But from the feeling, the basement is dry even on close inspection. Even the neighbors (it is a semi-detached house) cannot remember any water damage. I think one would have noticed that. Maybe it was already dried out by the builder before handover?

Well... all speculation at this point. How old is the house? Rivers, streams, lakes nearby? Groundwater level? I think I would only feel comfortable if I took a look into such a hole. Professionally sealed definitely looks different to me.

Borrow the measuring device and measure.

Otherwise, if it is dry, you can flow over it without problems.

Where can one rent something like that?

Where can you rent something like that?

Tool rental. Bad people buy a professional device on the internet, use it, and then send it back. Please do not do that.