A perimeter-overflow pool is a type of vanishing-edge pool designed so that water spills over all four walls, giving it the appearance of a mirror.
To create this effect, the tops of all four walls are set lower than normal, so they sit slightly below water level. This way, water spills over the entire perimeter and into a containment vessel, from which water is recirculated back into the pool.
These pools often are set at ground level, with water dropping through a slot or grate and into underground gutters. A simple slot in the decking has become more popular, because it barely affects the appearance of the deck.
A perimeter-overflow pool, or parts of it, also can be elevated higher than ground level, so that the water spills over the raised walls and into an open catch basin, or through a grate or slot leading to a gutter.
If the gutters or catch basin can't be made large enough to contain all the water, a remote holding tank may also be installed.
Because surface water doesn't have a chance to bounce off the walls like in normal pools, perimeter-overflow pools have the most calm, reflective surfaces. Hence, people will compare them to a mirror on the ground.
They are very popular for use as reflecting pools or ponds or in any setting where you want to reflect the sky and surroundings.
Because of their sleek finish, they also are found in many contemporary designs.