To be fair, VictoriaLuv said "Banish/Water/Water II", not just "Water/Water II".
So it could be similar to Stone->Stone 2-> Stone 3->Stone 4->Glare, where you start with Water spells, but at level 72 they become Banish.
But...where is banish in the trailer then? I don't know...From what I can tell, the WHM cast three single target abilities.
The first one is obviously the DoT. Then probably Glare 2. But the third one...the animation seems similar to the one of Glare 2....but on the particle effect it also seems to mirror the one from Glare 2.
So...it's not exactly the same? could it be something else? Or is it common for spells to have different particle effects if you cast them multiple times? I don't even know... (the difference is really small. On the first cast you can see 2 particle effects flying to the right and one to the left. The second cast you can see 2 particle effects flying to the left and 1 to the right)
Or maybe I am just reading too much into it because I watched the job action trailer for WHM a few time after reading this 'spoiler'.