Lots of flood cars run & drive. They are still generally worth 35-50% less than a non water car.
Buying one is an invitation to future problems and expensive repairs. Flood cars can go years with no problem and then not start and it can cost thousands to diagnose & fix the problem.
Many lenders will not lend on them. And that's why disclosing flood cars, like prior salvage titles is required.
Usually, a flood car IS a prior salvage because of the flood.
In rare instances, a prior salvage can be a theft recovery. I had one like that. The car was stolen, the insurance company paid it off and the car was later recovered & resold as salvage because they had paid It off.
I went over it very closely expecting to find damage because usually there is. This car had none. It had a different color steering wheel column and I was told one of the windows was replaced. (The criminal broke in to steal it and tore the steering column up to hotwire it.)
Finally, if you buy it, you will have to disclose it even years later when you sell it or trade it. And that will reduce the amount you will get by 30-50%.
So, its a BIG WARNING sign and a risk. But if you are lucky, it can be a good deal.
If you are unlucky, your car quits on the freeway, you tow it to a mechanic who cant find the problem. So you tow it to the dealer who cant easily find the problem and will want $150+ an hour to search for it. Plus whatever to repair it IF they can find it. And it can take many hours for even experienced mechanics to find. The problems are usually electrical and that's a big risk.
I dealt low end cars for a dozen years. I bought & resold about a dozen prior salvage from body work cars, but NEVER a flood car.
They scared me too much.
I dealt in cars that cost me $800-2500 cash and I tried to sell for $1500-3500 cash. (In a perfect world. I often made less)