because of condensation
Inspect the roof of your car and to find the source of the leak. Ask a friend to stay inside the car while you spray water over the roof. Your friend should be able to identify where the water is coming in.Check common problem areas, such as the seal around the windshield or sunroof and the drain tubes
Could be a head gasket problem.
The heater core or hoses to it are leaking inside your car
you have a leak in your heater core which is attached to your radiator and heats the air inside your car interior
There is a conditioning system drain hose. Eventually it starts to leak inside of the car. Fix the hose.
If your car smells of petrol inside, and you have not been using a petrol-like solvent to clean something inside the car, you probably have a fuel leak and should have the car checked by someone able to detect and fix a leak.
if you have a gas leak.
make be there is a gas leak
I am assuming you have a leak inside your car. If that is the case you probably have a heater core leaking. If that is not the problem please ask again with more specifics and I'll try to pick up for you.
usually due to Engine Oil problem. or even the radiator has problem like no water inside or it is broken