Infinity-edge pools create the appearance of a sheet of water falling off over the edge of the pool, giving swimmers the illusion that they are swimming near the edge of a waterfall. In reality, the edge of the pool is set just slightly below the pool's water level, so that the water spills over into a catch basin. From there it is pumped back into the pool.
An infinity-edge pool is most impressive where the vanishing edge seems to merge with the sky or with a large body of water. For this reason, they are often situated on hillsides overlooking the sea or a lake, or on the rooftops of resort hotels. Their construction usually requires considerable structural engineering and can cost a great deal more than a conventional pool. While the principle of an overflow catch basin is simple enough, designing one of sufficient size can be complicated. Inadequate water-leveling systems and improper waterproofing of the overflow edge also creates serious problems. Infinity-edge swimming pools date back to the 1950s, but infinity-edge spas and fountains have been around for centuries. The concept is thought to have originated in France. A notable example of an infinity-edge fountain dates back to the early 1600s at the Palace of Versailles.