Infinity Edge Pool Design

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 ("bather displacement") more water than the catch basin can hold. This can lead to catastrophic landslides or hillside erosion. If the basin is too large, 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.
Dedicated filtration systems are required on both systems. The edge pump is usually a much larger pump, required to overcome bather displacement, water in transit, and to raise the upper pool's level. It would be a waste of energy to run such a large pump as a primary filtration system. Adequate filtration is required on the edge-system (based upon the edge-system flow rate), as most of the debris flows over the weir and into the catch basin. A smaller circulation pump can be used for daily filtration on the main pool. Failure to install filtration on the edge-system will result in the debris in the basin being blown back into the upper pool.