Nationwide, only 20% of American homes at risk for floods are covered by flood insurance. Most private insurers do not insure against the peril of flood due to the prevalence of adverse selection, which is the purchase of insurance by persons most affected by the specific peril of flood.
Flooding occurs in moderate-to-low risk areas as well as in high-risk areas. Poor drainage systems, rapid accumulation of rainfall, snowmelt, and broken water mains can all result in flood. Properties on a hillside can be damaged by mudflow, a covered peril under the Standard Flood Insurance Policy. In high-risk areas, there is at least a 1 in 4 chance of flooding during a 30-year mortgage. For these reasons, flood insurance is required by law for buildings in high-risk flood areas as a condition of receiving a mortgage from a federally regulated or insured lender.