Easy Hydrophobia with a Priest

[Ciris]

While doing the Hydrophobia achievement have a priest levitate you and the water on the ground won't do damage to you.

The debuff applied when the boss dies WILL take off your levitate so make sure you're not standing above water when it happens.

This way you're actually able to contribute instead of just standing outside of the boss room .

[Hotsoup9]

Like to add that when you engage the boss, sometimes when you go around him from the water to the edge of a "platform", you'll dip down into the water and then come up toward the edge and you can get caught on the lip of it and you'll take damage. So it's best to get levitated and then stay on the of water ring around the boss. I don't remember losing my buff before I got the achievement, but if that's the case you'd have to move out at the end.