Many people find out too late that they are at risk for flooding, and even worse, that their property insurance doesn't cover flood damage. In fact, flooding occurs in every state; and six out of every ten Presidentially declared disasters involve flooding.
Many people believe they aren't located in a "flood zone". The reality is that they are in a flood zone, albeit a "low-to-moderate risk" zone. Flooding doesn't have to occur from a nearby body of water. A flood is defined as "a general and temporary condition of partial or complete inundation of two or more acres of normally dry land area or two or more properties (at lease one of which is your property) from: overflow of inland waters, unusual and rapid accumulation or runoff of surface waters from any source, and mudflows."
So if your neighbor with the slightly more elevated yard accidentally perforates their 18' above ground pool and sends about 9500 gallons of water gushing through the neighborhood, flooding your basement in the process, this would be considered a "flood". It wasn't from a natural body of water, but it was sudden, unexpected, and caused the partial innundation of 2 or more properties (his and yours) of normally dry land. Without a flood policy, it would also not be covered under your standard commercial property or homeowners policy.
If you do elect to purchase Flood coverage, there is a 30 day waiting period before the policy will go into effect, unless you're in a designated floodplain or are required under the terms of a mortgage to purchase the coverage.