The uncompressibility of water allows pressure to create a fountain.

Water's lack of compressibility helps to push water out of water hoses (handy for putting out fires), water pistols (handy for bothering Dad), and in artistic water fountains (handy for relaxing). In these instances, some pressure is applied to a container full of water and rather than compress, it comes shooting out of an opening, such as the end of the hose or the end of a small pipe, as in this fountain. If water was highly compressible, it would be harder to create enough pressure for water to shoot out of the nearest opening