I am on survival mode, and I looked into the eyes of an Enderman while in the water, and it did attack, but after a while it stopped and then just began to follow me. Why did it do this?
According to the Minecraft Wiki, Endermen become neutral once damaged by water or lava.
Endermen will continue chasing a player until they are either killed, sustain several hits, or become distracted by exterior elements like rain, fire, or sun; they are likely to teleport away to underground locations, such as caves and mineshafts, at day break.
As far as I know Enderman cannot teleport into water or into thin air with no blocks. As long as there are no blocks around, or on top the water the Enderman should not be able to follow you or teleport to a block near you.
Here is a question that can help answer some of your questions in further detail that was posted on the Minecraft forums page (Link)