The AC evaporator drain hose may become dislodged and cause a water leak on the passenger floor.Google+
Car Problem Reports
Scion xA Water Leak Due to Plugged AC Drain
Scion xA Problem
Average Mileage: 78,500 mi (17,000 mi - 140,000 mi)
Visitor, 2004 Scion xA, 140,000 mi
I have this issue too! Anytime it rains the water comes up and settles behind the driver's seat. It settles in the carpet and my car smells terrible.
I have the same problem now. By any chance do you know how much it was to get it fixed.
Visitor, 2006 Scion xA, 17,000 mi
Had to have it fixed (unclogged) 3 times. It started after the first summer and has happened almost each summer when I've used the air conditioner.