While hot water tanks and broken plumbing may flood a basement, the typical flooded basement is caused by undiverted rainwater, a basement below the water table, or saturated soils around the foundation. The first lines of defense against flooding are proper grading, properly diverted downspouts, a foundation drain and foundation waterproofing. The last defensive stand is the sump pump.
A sump pump should be covered to prevent evaporation and moisture buildup in the home, have a perforated drain in case of flooding, and have adequate discharge for the main pump and additional backup pumps.
Pumping the Sump
A sump is a basin or pit located below the basement floor that includes a container and a pump to remove standing water. Some homes also have a perforated drain system around the foundation that directs water to the sump. Others may only have a sump that collects the groundwater around it as it flows into that area naturally. Some homes have no sump at all.
The perforated sump container is surrounded by coarse gravel that filters out debris as water enters the container. The sump pit cover prevents anything from falling in and moisture from flowing out. The system's pump sends accumulated water through a pipe to the outside and away from the house.
Whatever sump pump is used, it should have a check valve on the sending or discharge pipe to prevent water from flowing back into the basin once the pump turns off.
For details on the different types of sump pumps and their uses, continue reading on Renovate Your World.