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

In reality the edge of the pool terminates at a weir that is 1/16 - 1/4" lower than the required pool water level. A trough or catch basin is constructed under the weir. The water spills into the catch basin, from where it is then pumped back into the pool.
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.