[header] How to dehumidify a car [title] Vacuum up lots of water with a wet/dry vac. [step] If your car is soaked or if there's a lot of standing water, you'll want to start by getting that out. Use a wet/dry vac to remove the excess water. 
Take off the top of the vacuum and remove the dry filter. Then plug in the vacuum and start sucking up the water! [substeps] If you don't have a wet/dry vac, you can rent one from a hardware retailer or an appliance rentals center.