The design options for fountains and water displays are multitudinous. There are practically no limits placed on the artist and designer. However, three main areas can easily be defined. On one, there are installations in which the element water plays the dominating role and the practical, sculptural design follows behind, in another, those in which the artistic design and formation of the fountain is of central importance and the water has only a supporting function. The third and main area is formed by any installation in which the water and the known design play an almost equal role and mutually reinforces each other in its effect. The more individually fountains and water displays are designed, the more important it is in the planning to concern oneself with the hydraulics; under calculated water volumes or incorrectly dimensioned components and leads make the installation defective for its whole life. Previously, fountains and water displays were supplied and operated from springs or drinking water systems; once the water passed through the system, it was lost. Almost exclusively to-day, re circulating systems are employed. Once a basin is filled, the water is used over a longer period and re circulated again and again by means of the systems pump. Only after it is contaminated is the water drained off, the fountain unit cleaned and refilled. The intervals between water changes can be substantially extended by using a filtration system. Water loss due to evaporation or splash, is usually replaced automatically from the drinking water system. The pumps used are either submersible motor pumps or dry-mounted centrifugal pumps which are installed in a pump chamber or in a cellar.