We can't stress this enough: many people assume that their homeowners policy includes flood coverage.
It doesn't. Standard homeowners-, renters- and business policies do not cover flood damage. If your property is in a flood prone area, you should strongly consider buying flood coverage.
How do you know if you're in a risky flood area? Type your address into the red box on the home page for the federally run National Flood Insurance Program. That's where most people buy their flood coverage. Many local insurance agents sell these policies.
And if you think a few inches of water wouldn't cause much damage, you might be surprised. The NFIP put together an interesting interactive simulator that details -- item by item -- the costs of different levels of flooding in a typical home. See the link above.