Water compressibility allows water fountains to spray water.
One property of water is that it is not compressible--you can't press on it and have it shrink much at all in volume. Just fill a balloon very full with water and then really squeeze it (to compress the water). Instead of the balloon shrinking in size you will end up taking a bath.
Being incompressible, water makes a handy and useful tool for people to do work (and have fun). Water incompressibility allows fire hoses to work, makes hydraulically-driven tools to function, and for kids to have fun running underneath a fountain that shoots out water (under pressure).
>> Learn more about water compressibility at the Water Science School.