This USK 4SDM318 Submersible Pump is engineered to be lowered completely underwater into a deep narrow well—specifically a borehole or a deep well with a minimum diameter of 4 inches (100mm).Its main purpose is to push water upward from deep underground water tables to the surface. Because it is a multistage centrifugal pump, it uses stacked impellers to build enough pressure to lift water over long vertical distances