Water Magic

Water Magic is an Elementalist secondary attribute meaning that any character with an Elementalist for their primary or secondary class can put points into this attribute.

Guild Wars Description
"No inherent effect. Many Elementalist skills, especially spells which deal cold damage and slow and hinder your foes, become more effective with higher Water Magic."

General Description
First off, the name Water Magic for this attribute is a bit of a misnomer, since the vast majority of the spells within this category involve ice. In fact, the only Water Magic skills that don't involve ice or deal cold damage are the skills Rust, Mist Form, Armor of Mist, Swirling Aura and Blurred Vision. However, Water Magic is a very powerful attribute. Water Magic spells may do less damage per hit then their equivalent Fire Magic or Air Magic spells, but they also usually slow down or hinder their foe in some way at the same time. Water Magic spells are also more versatile; there are quite a few skills that help protect the caster from harm.

First off, the skills that deal damage. As earlier stated, these usually have a secondary benefit, making Water Magic one of the most interesting attributes. Deep Freeze, Frozen Burst, Ice Spikes and Shard Storm all deal large amounts of cold damage while at the same time slowing down your foes. This is extremely useful as a slowed-down foe cannot reach you as easily, allowing you to rain more spells down at a distance. Water Trident is unique in that, while it does not slow down a foe, it knocks over the target if it is moving. This fact combined with Water Trident's low energy cost, casting time, and recharge time make it one of the best skills in the game.

But Water Magic, unlike Fire Magic, doesn't stop at direct damage and conditions. Many Water Magic skills protect you from harm. Swirling Aura helps you avoid all projectiles, while Blurred Vision hexes groups of foes to miss with their melee attacks. Combined with Armor of Frost and Armor of Mist, not to mention using Ice Prison to slow down an attacker to a crawl, makes it unlikely anyone will be able to beat you as long as you have a way to heal yourself (which Water Magic lacks).

A Water Mage's worst fear is a Mesmer using Domination Magic, who can remove Water Magic hexes, shatter a Water Mage's enchantments, and counter the direct damage spells. The best strategy to deal with them is simply having another player in your group focus on destroying the Mesmer while he is focused on killing you, but if that is impossible, try engaging the Mesmer in melee combat (a Warrior secondary class would help for this).