Actuarias,
As Chippy says this is quite normal, especially in hot weather when the air con is working hard. It is water removed from the air taken into the car as part of the cooling process. You normally don't notice it as the vehicle will disperse the water as it moves. However, if you remain stationary for a period of time it will pool under the vehicle.
For my work I have to use a number of different makes and models of vehicle(they all do it) and the car is my office. So, I can be parked up for long periods with the air-con running. Frequently I will get a tap on the window from some kind person explaining that my car is leaking petrol, etc. Happened yesterday, the water was pouring out of a Ford Kuga, and the bloke was really concerned that I was about to go up in flames. Even when I explained it was just water he looked at me like I was mad and about to die in a massive inferno! Brave or fool-hardy people though to approach a car they think is leaking petrol!
http://www.airconcars.com/html/how_it_works.html