Sump pumps are also used for high water tables: the basement floor is lower than standing water in the ground. The water always exerts pressure on the basement floor until it finds a crack in the concrete. That under-the-floor drainage pipe to the sump pit just constantly drains the rising underground water, and the pump gets it out of the house. My last house in Illinois had a sump pump that ran consistently (5 minutes off, 30 seconds on) even in the driest of droughts.