Ruined is a subjective term.
Flooded car floor.
If the water in your car was dirty wash off the carpeting and floor mats with clean water.
Most insurance companies will consider the car totaled damaged beyond economically reasonable repair if water reaches to the bottom of the dashboard or higher.
Since everywhere else is dry i believe there must be a leak on the chassis floor.
This is when distinct problems can begin to occur.
If this is the case then have your car towed to a mechanic for a professional assessment.
Even if invisible water can get into the small spaces of your car and remain there causing mildew and mold formations.
Use a pressure washer if you have one available or use a garden hose with a full stream of water.
Wash the carpets until the water runs clean off the carpet.
If possible hang the carpets up to wash them off and let the dirt run off easily.
If floodwaters were more than a few feet deep water probably made it to the inside of your car.
An owner might consider his car ruined even though the insurers might not deem it a write off.
Mud and debris usually leave a waterline on the car inside as well as out.
If your car is poorly or improperly sealed it s likely to suffer from flood damage after a hard rain.