Do you have anything in mind?
What is your specialisation?
You could do a lot in fountains. Let me give you some brief idea here. Since you mentioned Arduino, I’ll assume you want to have control over the fountain to create visual effects.
You could build an Animated Fountain.
These fountains are dynamic and change patterns with a predefined delay. There’s no need to sync with music.
The next type is Musical Fountain
Musical fountains are also a type of animated fountains but they sync with music. The synchronisation could be achieved by preprogrammed sequence.
The next type is Self Choreographed Musical Fountains
These aren’t common as not many have been able to achieve pleasing patterns. This requires higher amount of processing to be done and is very complex. This is where I have mainly worked. I have been able to achieve good results.
Here’s a video of what I could achieve. I’m hoping to build another fountain soon and demonstrate my algorithms well with it.