Drywalls are meant to stay dry, so any moisture can damage them and lead to moisture to turn into mold growth. If you have experienced a flood, you will need to act fast. Drywall will begin to deteriorate when moist, and if so, it will need to be replaced.
If walls are wooden, or other materials, it is likely that moisture will damage them as water will cause wood rot, will lead to mold development, and lead to a need for extensive repairs. When you have a flood, it is best to hire a professional to manage these expectations and take on the liability for resolving the issues in a timely manner.