Call your insurance company. And do not be optimistic.
The truth is that it’ll depend largely on the car, how deeply it was submersed, AND THE WATER. For example, jeeps are designed to be washed out with a hose; Mazda Miatas are not. The jeep would fare far better if partially submerged…although I still wouldn’t want to buy one that had been. And any vehicle submerged in water contaminated by sewage is pretty much ready for the crusher. The potential problems are right out of a horror movie.
And that raises a good point for those looking for used cars…BE CAREFUL. Many of these vehicles WILL end up on the used car market…in states across the country. God must love unethical people, 'cause he made plenty of 'em and they’re everywhere.