Young Blonde Girl Posing In The Infinity Edge Pool At The Sea

Circulation systems
Properly built, these pools have two circulation systems. The first functions like that of a regular pool, filtering and heating the water in the main pool. The second circulation system (known as the "edge system" or "effects system"), filters the water in the catch basin and returns it to the upper pool. When the edge-system stops, the water level in the upper pool continues to spill into the basin - stopping at the level of the weir wall. The water necessary to raise the upper pool and fill the edge-system plumbing is called the "water in transit." Considerable skill is required on the part of the designer to incorporate a catch basin of an appropriate size.
If the catch basin is too small, swimmers will force out water ("bather displacement"), more than the catch basin can hold. This can lead to catastrophic landslides or hillside erosion. If the basin is too small, the edge-system pump may also draw down the catch basins' level, before the water has returned in sufficient quantity for the edge pump to retain its prime. The catch basin also needs to have additional holding capacity (above its static level - known as "freeboard"). The freeboard is the available extra capacity to hold the bather displacement and rain water, before it reaches the level of the overflow line.