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.

Tis is nothing more than regular construction physics. This is the phenomenon of dew point condensation.
If you bring warm and moist air into an underground parking to ventilate, then the brought in moisture can condensate on the cold floor.
If you bring the outside air with a temperature of +33°C and a relative humidity of 65% through an open garage door or ventilations, the present moisture condensates on every surface colder than +25,5°C. When the outside temperature is +25°C and the humidity 85%, you get a dew point condensation on a surface colder than +22,3°C. The floor of a parking rarely gets warmer than 22°C. Because of this the brought  in moisture condensates on the cold floor.

You can use the dew point calculator for free.

You can find the relative humidity of the outside air here: https://www.bdb.be/