Flooding is no joke, and is responsible for over $5 billion worth of property damage a year. Bear in mind that when we are talking about floods, we aren't talking about the sort of damage caused by hurricane storm surges and tsunamis in coastal areas. These present an additional set of risks that are not covered here. Flooding otherwise refers to the sort of damage seen from heavy rain or melting snow in low lying area, especially next to rivers.
If you live in a low lying area, especially near a river or water source, be sure to read Ray Gibson's excellent Insuring Against Floods. Flood insurance is a complicated thing, and is often NOT covered by normal insurance policies. Please be sure to read this to determine if you are at risk and what options you have.