What are the common areas for water to accumulate in under the carpets, and what is the solution to this?

Right now, I know that under the drivers side storage bin is wet, and behind the drivers side tail light is wet. Fortunately there's no rust yet, but im sure its coming.

Common causes?

 

if you have a sunroof, check the drain tubes under the headliner for tightness and for cracks and plugging or breakage. that will cause the water under the bin as will bin rust allowing the water to acculumate after a drive in the rain. water behind the lights is a sure indcation of a faulty drain tube on the hatch channel or rusting of the metal lip under the hatch seal. remove the rear center carpet and plastic and inspect the drain lines for tightness and for cracks and plugging. also check the gaskets under the hatch strut "nut" on the outside of the window glass. these often shrink or deteriorate and allow water in during a rain storm.

 

check your tail light gaskets themselves, mine leaks from there