Water on the base plate

Hello everyone,
we were on site yesterday and saw that there are large puddles especially in one room. Now I wondered where they come from, since the ceiling is already in place.
I have to say, it rained heavily the day before, one might think that because there are no windows yet, the rain just came through. Could be.

What surprises me, however, is that the adjacent kitchen has no water on the slab. Ok, there is only a patio door on the wall and the living room with the windows has two large windows. But everything in the kitchen is dry. And when I go upstairs, the ceiling is more or less dry too, even though our shell construction still has no roof and it is said to have rained.

Could the water come from under the slab? Or water that seeps around the house or does not seep properly and gets into the slab and presses up from there?
It can’t be groundwater; that is about 30m deep.

Strange... Or harmless and just rainwater?
Maybe someone has an idea? Or an explanation.

The base plate will be uneven. Probably not visible to the naked eye in dry condition. Water is also known to find its way. Do you see any small water flow anywhere?

The rain does not come into the house equally from every side, so it is not equally wet in all places. And otherwise, as says, water always finds its way down.

If the sun shines through occasionally, it also dries faster on top.

Yeah yeah, the base slab will not be even, hence the puddles. But where the water comes from is a mystery to me. Ok, if it rains, it comes through the windows. But then why is the kitchen dry, the room is next door (in case of driving rain from one side). And the floor of the upper floor is also more or less dry. At some spots wet from rain, but no puddles.

Yeah yeah, the floor slab won't be level, hence the puddles. But where the water comes from is a mystery to me. Ok, when it rains, it comes through the windows. But then why is the kitchen dry, the room is next door (in case of driving rain from one side). And the floor of the upper floor is also more or less dry. Wet in some spots due to rain, but no puddles.

because it is uneven there and possibly dried up hmm