Well, if you all ready spilled it, go ask your downstairs if you can look. LOL

Really, though, it all depends on the carpet and pad and floor underneath and how the water spilled.

If you spilled, say, a bucket of water and it got a large area wet then probably any damage would be limited to your apartment. If it was something more like a leak, the water could make it down to the apartment below.

The best thing you can do is lift up the carpet and put a fan on the wet spot and get it dry ASAP. If you leave the wet carpet on the floor it will probably warp the floor underneath if it is wood and also mold.