Water Magic: 12 (10+2)
Energy Storage: 13 (10+2+1)
Water Magic: Water Trident (elite), Shard Storm, Ice Spear, Ice Prison, Armor of Mist, Water Attunement
Curses: Spinal Shivers
Other: Ressurection Signet
Weapon and Armor:
I always wonder what kind of armor should I take on Arenas. There is only small difference between them - bonus vs. elemental damage. It's hard to say what kind of Elementalist you will face with so take this one you like. ;)
For weapon use Staff with bonus to energy and HP. Staff should have "Improve skill cast/recharge using Water Magic".
How to play:
Right before fight cast Water Attunement to save some energy.
This build was made to interrupt casters so find one. Best choice would be Elementalist (long casting time) but other casters are good too.
Cast Spinal Shivers on your target and Ice Prison so he couldn't escape. Then start spamming with Water Trident, Shard Storm and Ice Spear. It would be good to come as close as you can to your target to reduce distance - Water Trident and Ice Spear will have shorter flying time.
Good used this build can be best interrupter ever.
Use Armor of Mist to defend yourself and run.