In terms of killing mold after a flood, your first choice should be to go for commercial mildew and mold removers.
If you want, you can also choose tri-sodium phosphate (5 Tbsp. every gallon of water) or washing soda.
Last but not the least, the solution of water and bleach can also be picked (1-quarter cup of the laundry bleach per gallon of water).
Make sure to use proper precautions as well as security equipment for the mold remediation process while cleaning with tri-sodium phosphate, bleach or any other heavy-duty cleaners.