More often than not, basement flooding is a result of overland flooding, infiltration flooding or sewer backup, or a combination of two or all three of these types of flooding.
After a few days of steady rain, when spring snow-melt occurs or during an extreme rainfall event, the soil around your home can become saturated with water. Steady snow-melt and precipitation can also raise the ground water level to a point where it is higher than your basement floor.
This groundwater can infiltrate into basements through cracks in basement walls (or foundation walls) and cracks in basement floors. Infiltration flooding can be a significant problem in older homes where mortar has weakened over the years and cracks have developed in stone or cinder block foundations.
Homes that do not have a weeping tile, where the weeping tile has not been maintained, or where there is poor lot drainage also have a greater chance of suffering from infiltration flooding.