In a city-wide flood situation that includes sewer back-up, how can you prove that the sewer backed up before the home was flooded? Or does it matter? I have a homeowners policy w/ a sewer back-up endorsement but no flood insurance. If I can prove the sewer back-up happened before my home was flooded, will I have a claim?

If you can prove it happened before the flood ( and not because of the flood but back up for a different reason)

You would have a claim but only for the amount of damage from the back up, not for any additional damage done by the flood.

Will be hard to prove, witnesses ? Expert testify in court, since the insurance company will almost for sure deny and want to go to court over it.