Skimmer is designed to extract water from the surface of the swimming pool. It prevents leave floating debris etc. from sinking to the bottom of pool. The debris is caught in the skimmer basket and the water is sent through a pipe located at the bottom of the skimmer, through the filter pump. When the pool pump is turned off, the flapper floats into closed position preventing debris from going back into the swimming pool.

A skimmer can also be used to vacuum the pool with a manual pool vacuum or suction side automatic pool cleaner. When the pool pump is on, the pipe below the skimmer basket creates suction.