I have a 1953 ranch with daylight basement. Pictured below is the point where (I believe) the water main enters the house horizontally (water meter is out in front lawn at ground level, aligned with this entrance). Upon entering, there is a T branch. Upwards pipe goes to a shutoff valve, while the downward branch disappears into the floor and is upstream of the shutoff. I can't figure out why this was done this way. It's possible I have it reversed and that supply comes out of the floor and then goes back out of the house at the T, again before the shut off valve. I am trying to track down the many possible causes of a damp floor in this area and would like to understand why this was done this way before going further. Thanks in advance!
UPDATE: I have called a plumber (I don't want to DIY myself into a bigger mess on this particular project) and will update once I get an answer.