I have had some problems with the floor on the front passenger side of my van being very wet at times. After it rains I could sometimes even hear water sloshing around. Then on one occasion I saw what looked like a small waterfall coming from somewhere behind the glove box. The passenger side seat was even starting to rust around the base from all of the water.
The problem is that the windshield wiper assembly has a tray under it to collect water. Then a drain hose connects to the bottom of the tray to drain the water out. However that hose can get so clogged that the water cannot get out. Eventually it spills into the passanger side floor. The solution is to pull off the hose (it is dead center in the picture below) and then clean the garbage out of the drain hose.