ᐅ Water on the foundation slab

Hello everyone,
we visited the site yesterday and noticed that there are large puddles in one room in particular. I was wondering where they could be coming from since the ceiling is already installed.
I should mention that it rained heavily the day before. One might think that, because there are no windows installed yet, the rain simply came in directly. That could be possible.

What surprises me, however, is that in the adjacent kitchen, there is no water on the concrete slab. Okay, there is only a patio door on the wall, and the living room with windows has two large windows. But the kitchen is completely dry. And when I go to the upper floor, the ceiling there is also more or less dry, even though the structure doesn’t have a roof yet and it’s said to have rained.

Could the water be coming from underneath the concrete slab? Or could it be water that seeps around the house or does not drain properly, soaking into the slab and pressing up from below?
It can’t be groundwater since that is about 30 meters (100 feet) deep.

Strange... or is it harmless and just rainwater?
Maybe someone has an idea or explanation.

The concrete slab will be uneven. It probably won't be visible to the naked eye when dry. As is well known, water always finds its way. Do you see any small water flow anywhere?

Rain doesn’t enter the house equally from all sides, so not all areas get equally wet.
And otherwise, as @HilfeHilfe says, water always finds its way downward.

When the sun breaks through occasionally, the top layer also dries faster.

Yes, the slab won’t be perfectly level, which is why there are puddles. But where the water is coming from is a mystery to me. Okay, when it rains, water comes through the windows. But then why is the kitchen dry, even though the room is next to it (in case of wind-driven rain from one side)? And the floor of the upper storey is also more or less dry. It is wet in some spots due to rain, but there are no puddles.

sauerpeter schrieb:
Yes, the concrete slab will not be perfectly level, which explains the puddles. But where the water is coming from is a mystery to me. Okay, if it rains, it comes in through the windows. But then why is the kitchen dry, the room next door (in the case of wind-driven rain from one side)? And the floor on the upper floor is also more or less dry. Some spots are wet from rain, but no puddles.

because it is just there and possibly has dried up

hmm