For public pools of all kinds, pools with overflow-channels are a part of the German DIN directions. Even for private pools, pools with surface aspirators (skimmer pools) are displaced more and more by overflow-systems.
The water level is the highest point of the pool. Overflow and displacement water flows in an overflow-channel, further through a collecting pipe into a collecting tank. Also the freshwater is fed here which is necessary due to evaporation and for hygienic reasons.
The water is carried to a filter system via pumps and afterwards where necessary heated, disinfected and inducted back into the pool by nozzles of different shapes.
Overflow pools have a higher need of space at the same size of skimmer pools. They are more complicated to produce and are therefore more cost-intensive compared to skimmer pools.