2008 Camry - I really thought it was from rain, because I noticed it after several rain storms. Lots of water under carpet. Dealer said it was clogged AC drain.
What is the best way to dry? To stop the mold. Don't want to spend $1300 for new carpet, Platinum Extended Care won't cover it.
If it smells like anti-freeze then you may have a leaking heater core, like I have.

If it does not, and it's wet after several rain storms then it may be the following: possible clogged sunroof drain vents or maybe the ac drain.
Do you usually park with your sunroof open or tilt under trees or close by to trees? If so, then the sunroof drains may be clogged some. What about your headliner, is it wet anywhere??
The best way that's working for me is to remove the door sills/footwell plastic moldings etc. pull the carpet back to reveal the floor board then stick a couple large objects under the carpet to keep it off of the wet floor board and keep your windows open to let air circulate. It's nice and hot outside so it should dry relatively quickly. If you have a wet/dry vac then i'll spray some Lysol on the carpet then vacuum it up then let it dry naturally.
Also try this, open your sunroof fully, then pour some water down the sunroof drain holes and you should see it drain below just to the rear of the fenders.
Let me know how this works out for you.