I have 2012 G37 sedan with water leak which forms on drivers side under floor mat.Where is it coming from?

 

This is very common for the G37 sedan, it is almost always due to poorly designed grommets which connect sunroof drain tubes to the firewall (which are meant to run water out of the cabin, but in reality often leak water back into the cabin). There is one each in the driver and passenger sides, both prone to failure.

The most effective way to fix this is the “sunroof drain reroute” process, which is pretty well documented here:

You basically add some new tubing and using an existing A/C condensation drain tube (which is in the passenger side footwell) to entirely circumvent those faulty grommets.

Hope this helps / good luck with the project (I never worked on a car’s interior before, and it took me about 2 hours and $30 worth of materials). Worked like a charm for me.

Worthy to note, there is also an issue with leaking around the windshield wiper cowl. It’s relatively less common, but could potentially be at play in your car too. I’d do the sunroof drain fix, then if issues persist, look further into the windshield leaking (which usually occurs around the cabin air filter).