Voluntary flood insurance policies are not enforced until 30 days after purchase.
There are some homeowner endorsements that will cover a back-up or overflow of sewers or drains or a sump-pump. These type losses sometimes do occur during flooding events. These endorsements will often have dollar limits substantially less than the flood policy
Flood insurance is required by law for some high risk homes but only a minority of homes fall under this category. Congress passed some laws requiring that all federally-insured or regulated lenders, for instance mortgages backed by Fannie Mae or Freddie Mac require flood insurance to protect their investment in the property.
90% of all natural disasters have some form of flooding.
Collapse or subsidence of land and the insured house, along a shore of a body of water caused by waves or currents of water are considered a flood and are covered by this policy.