Numbers tell the tale
To measure the present moisture in walls and floors a reliable moisture meter is necessary. A moisture meter with two pins is pushed into wood or other soft materials so the electric resistance can be measured. The same can be done with an analogue or digital Ohm meter. On hard surfaces like bricks, tiles, joints, concrete, natural stone, ... this doesn't or barely works. The pins cannot be pushed into the material. There are other devices on the market for there materials.
Wet spots on the walls
When discovering wet spots on the walls, many people invariably think of rising damp. The wet spots on the walls are only an observation, a superficial visible phenomenon. After a thorough analysis it seems the so-called rising damp does not exist.
Condensation with warm and sultry weather
With warm and sultry weather condensation on the floor of an underground parking (or another cold floor) can occur.
This phenomenon occurs everywhere a few times a year. Many little drops form puddles of water, so it seems that the underground construction leaks.