mystery water in floorboard?????

in the driver side floorboard, front seat only, i have been finding the floorboard really wet. its not so bad that there is standing water though. it only seems to happen when it rains, but i cant find a leak or any evidence of a leak from anywhere around the doors or windshield. someone said it may be a hose backed up somewhere????? any help or any ideas are greatly appreciated. thanks!