With default affinity, I didn't find the water spells to be any more tedious than the rest of them.

The only thing that bugged me was the fact that the only places I could think of to effectively spam it where also places I always look for Invokers in my PK range, so I felt pretty unsafe doing it. I think I perfected drown in one session though, maybe two. Generally, I think I managed to stick with my "perfect at least one spell per session" goal fairly easily.