What Causes Water Under the Rear Seat Car Mat?

[StEmiliano]

Water under the rear seat car mat may be caused by various reasons such as a leaking drain plug at the bottom of the car compartment, a leaking sunroof drain pipe, a leaking door, a leaking heater core (causing antifreeze leakage), a damaged or improperly installed air conditioning drain pipe, among other possibilities. There are multiple potential causes: sunroof leakage due to poor sealing—check the sunroof; water from car washing that wasn’t properly cleaned; or rust in the car’s small radiator (used for cabin heating), leading to leakage. To check if the sunroof drain pipe is clogged, fully open the sunroof to reveal a groove. Slowly pour water into this groove (the sunroof drain pipe) and observe whether the water drains properly or is blocked.