If, when you change the pollen filter, you notice there is water in the filter box,
it may be because the cabin air inlet vent is not draining correctly.
The 450 takes cabin air from the right service screen (as you look at the front of the car).
The service screens are the 2 vents either side, just below the windscreen.
It passes from right to left, through the cabin filter (if you have one) and into car.
Underneath the right service screen is a slide in insert which is supposed to stop
water running down the windscreen and into the air inlet duct. However, if the seal is
damaged or the insert isn't replaced, the cabin air inlet duct can fill with water.
What would normally happen now is that the water would pass a little way down the
air inlet duct before reaching the drain point for the system. The water would then be
safely guided back out and allowed to drip onto the top of the front undertray.
However, over time, it is possible for this drain point to become blocked with leaves and mud.
The drain fills up and the water passes through the cabin filter, into the cabin heater box where it could leak inside the car causing wetness under the footwell carpets.
The water doesn't go away, it just sits under the carpet. You may notice a smell, you might not. If the water is left there it will do some serious damage in the long run, apart from rusting exposed metal it will destroy the carpet.
The best course of action is to check under your carpets regularly for any moisture.
Clearing The Drain
The quick way if you have thin arms.