I have an '09 . There is a large amount of liquid accumulating under the driver's seat and in the passenger footwell behind it. Do any fluid lines eg windshield washer etc. run through this area? Any ideas?
Coolant is bright green, Water is clear, these are two I can think of that could get in to the car.
You may have a waterleak, do you have a sunroof? Find the highest point of the leak and trace the source from there. You may have a leak on driver's side B-pillar. Take off interior to check.
Hopefully you have this already fixed.
I'd like to inform you that the steering pump is infront of the engine near the front of the car and no steering lines run into
the passenger cabinet. Steering fluid for subaru is a red oil. But yes a missing rubber seal on the firewall from above hood level would seep rain water. Missing Rubber seal below firewall- less likely unless it's near cabinfloor and could seep (rain)puddle water.
Tracing repair/maintenance history would help diagnosis these problems if mechanics have worked in such areas and left something loose, of course general knowledge of your car is necessary.