My passenger back seat floorboard stays soaking wet. on 2009 Pontiac G6

All windows are up when it rained but even when there is no rain it is soaked, thinking maybe a/c but not sure. The carpet is so soaked i have mildew in carpet and it smells. Just wandering if there is a plug or something i can do or if this is gonna have to be put in shop(rather would like to fix myself)

Asked by for the 2009 Pontiac G6