Ok, big problem: There are hardly any good water elites in Cantha. Cantha doesn't have Mist Form, Ward Against Harm or Water Trident... all the good ones
.
Anyway here is one build i use in the random arena:
-Ice Spear (never leave home without it, fast, cheap and deadly),
-Icy Prism (damage and interrupts/disalbes signets),
-Frozen Burst (about 115 damage to foes around you and 10 second slow),
-Blurred vision (it's not blind but it lasts long),
-Aura Of Restauration (selfhealing is always usefull)
-Mist Form (elite, life saver, no warrior/ranger/assassin can hurt you)
-Water Attunement (for energy management)
-Res Signet (you know why
)
Now, this is a simple (not perfect) build wich can kill warriors with ease. Casters are dead after a few well aimed Ice Spears. One thing to keep in mind: Warriors/rangers/assassins can't deal damage to you in your mist form but they can give you conditions so be aware. Also, Mist Form only protects from attacks, not spells and hexes.
Other possible skills to take:
-Rust: tripples the casting time of signets for 44(!) seconds. throw it around whenever you can. Hexed foes need 9 seconds to use a res sig. this way you can interrupt them (after waiting a while) with icy prism. Also, warriors who use healing sigs are doomed due to the -40 armor while using it.
-Water Trident (elite): Nice damage dealer, recharges in 3 seconds and is very cheap. If it hits a moving foe, the foe is knocked down. This makes it very hard for enemies to flee or warriors to get to you. Very irritating
.
-Ice Prison/Tenai's Prison: With 16 water magic, hexed foe moves 66% slower for 21 seconds. Use this on warrior (wich become useless) or on fleeing monks, eles and other. Keep in mind that this hex ends when the target takes fire damage. Your teammates might use fiery swords or kindle arrows so taking this is a bit of a gamble.
-Armor Of Mists: If you don't have Mist Form, this is the spell for you. For 21 seconds you get +42 armor and move 25% faster. Both come in handy!
-Ice Spikes: Target and adjacent foes are hit for about 84 cold damage and are slowed for 66% for 6 seconds. Use on small groups only since it costs 15 energy.