Sorry, a little late for the party, just got back from vacation.
You are expecting imaginary water drops to fill up a cup. you could use collision effects so the water will lay on top of each other but I think for more realistic action, You really need to fake it, that is what it's all about.
You can create a volume and can raise it up as your particles go into the cup, try parenting your volume to a null and raise it over time, you can use another emitter to produce some bubbling turbulence for effect
Hope that helps if you haven't already taken care of it
