Water coming out of the air conditioning (AC) vent in traffic jams is a common occurrence and is typically not a cause for concern. The reason for this phenomenon is the condensation of moisture from the air inside the car's cooling system.
When you run the AC, it cools down the air inside the car by removing heat and moisture. As the warm and humid air passes through the AC system's evaporator coil, the moisture in the air condenses into water droplets. This process is similar to what happens when you see water droplets form on the outside of a cold drink on a hot day.
Under normal conditions, this condensed water is drained away from the AC system through a drain tube, and you won't notice it. However, in certain situations like traffic jams, the AC system may not be running at its optimal efficiency, and the condensed water can accumulate in the AC's ducts and pipes. When the car starts moving again after being stationary in traffic, the water that has accumulated may be forced out of the AC vents, causing it to appear as if water is "leaking" from the vents.
This is generally not a cause for concern as it is a normal behavior of the AC system, especially during humid weather or when the AC is operating under heavy load. However, if you notice a significant amount of water consistently coming out of the AC vents even when the car is moving, or if you experience other issues with the AC system's performance, it's a good idea to have it checked by a qualified mechanic to ensure there are no underlying problems with the AC system's drainage or cooling functions. Regular maintenance of the AC system, including checking the drain tube and evaporator, can help prevent excessive water buildup and potential issues.