Flooded and water drenched cars
Cars never respond well to going for a swim, and after they've dried out, you begin to get that awful stagnant water and mould smell building in the car, which gets worse the longer it's left untreated. Being able to fix this depends on how far the car was underwater - if the water has gone higher than the cars dash line, then at that point we say forget it, unless you are happy with replacing all the electronics, as the mould and old dirty water smells will be the least of your dramas over the long term.
If the water has not gone further than the lower parts of the dash, the best remedy we recommend is like above for extreme mould removal in carpet, except you will be pulling out the whole interior as far as how high the water line is in the car, thoroughly cleaning everything you pull out and washing the cars interior metal chassis with the Auto Body Gel in a bucket with a microfibre cloth to remove all of the grime and mud/silt that will be deposited in the floor, doors, sills, cracks and recesses. If the door trims went underwater and have evidence of mould, have them replaced, likewise if the seats have been under water, look at having the foam replaced in them as well. Steam clean everything you can, and finish the job after putting everything back in the car and spraying Pong-Go everywhere, especially if it's fabric.
If the smell is still there, look at doing a shock ozone treatment on the car, there is more detail about shock ozone treatment in a section below.