When flooding damages your water heater, for the safety of your home and family, repair is not recommended.
If your water heater has been underwater an inch or more, the sensitive safety components have likely been damaged beyond repair. Water heater manufacturers, Underwriters Laboratories (UL), The American Gas Association (AGA), and state Departments of Public Health all recommend replacing flood-damaged water heaters due to potential life safety issues.
If you have flood insurance, your insurance carrier most likely will reimburse you for the replacement of a flood-damaged water heater.
Always make sure that you use a fully licensed plumbing contractor to install your new water heater as required by state law.
Due to immediate corrosion, floodwater debris and potential damage to the gas control system, all liability for damages related to relighting a flooded water heater rest with the party that relights the unit.