Can you start the car after it went through flood water?

depends

if the water got into the air intake it may have been drawn into the pistons in this case when you turn the engine over the water will not compress as the piston rises and you may damage the engine

best bet on a petrol is remove spark plugs and turn it over manually if no water is visible in the plug holes then turn over on starter motor

with a diesel you have to remove the injectors

this is worse case you may be lucky

best of luck