My husband worked for coca cola for 12 years. I just asked him. He said in a restaurant (permanent location) the syrup is "tapped" into the water lines. The carbonation comes from the CO2 tanks which is a gas that gives it a fizz.
Now if you are renting a fountain server with the carbonated water, then yes you will not have it tapped into the water lines.
I think @ DW because of cost they would have it the permanent way.
Also, you must think of the ice.
HTH