There are a number of reasons why basements flood. Flooding can occur by seepage or flow through the walls or foundation floor, from surface water sources, or by a sanitary or storm sewer backup. Please remember:
Basements are inherently prone to flooding. They are, by definition, the lowest level of a building, typically built partly or entirely below ground level.
A crack in the foundation floor, provides gravity with a perfect path for water to be pushed into the basement.