It could be that your AC condenser drain hose is clogged or disconnected. Then, instead of the water collected by the AC draining out and to the ground, it dumps on to your passenger side carpet.

 

what he said

make sure to take care of it asap before the water starts to corrode your floorboard and/or any wiring in that area. (you're going to have to remove your seats and dry it asap, then find the leak and take care of it).