piece of architecture that ejects water

A Fountain is an arrangement, usually made by man; in it, the water from a source is captured in some way. Most often, it is used to fill a basin of some kind. Sometimes there are many basins, and water runs from one into the next. It is also common to have sculptures in fountains.

The Trevi fountain in Rome
The Jet d'Eau in Geneva

Sometimes jets are used to make the water go high into the air, using pressure.