In 1.12, you can actually abuse the Enderman AI by punching the mob while you are sitting in the water.  The Enderman will not join you in the water.

In 1.13 snapshots, they do.  They will jump into the water, attack you, then sit there dumbfounded instead of teleporting out as they did in previous versions.

I believe this is because of the new aquatic update, and the water isn't viewed the same way by their AI.

I can take a video, but this is pretty easy to reproduce.