Um...
- Get a pen or notebook type app.
- Jot down notes on several curses you might want for your game.
- Jot down some notes on a fountain descriptions.
- Compare the notes and select something that sounds awesome.
Like, how a player would go about creating a cursed fountain?
Buy a fountain and make it into a magic device trap with the craft wondrous item feat.
Decide on the Touch Trigger (with an alarm spell), so the trap only activates when someone touches the water in the fountain. This option does not have an extra cost increase.
Choose a spell which fits and pay the cost derived from the Magic Device Trap cost table.
So, a fun spell would be Aboleth's Lung, which makes target unable to breath air, but grants the ability to breath water.
A cursed fountain which would cast Aboleth's Lung on all who touches it would have a cost of 3000 gp, reset after 1 round, have a DC of 13, and a perception check of 27 to notice that the fountain is cursed.