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."
Though named Water Magic, this attribute is based on dealing cold damage and implementing ice-based hexes. While its spells may do less damage per hit than their Fire Magic counterparts, they usually slow down or hinder their targets 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.
Spells like Deep Freeze, Frozen Burst, Ice Spikes and Shard Storm can deal small amounts of damage while simultaneously hexing foes with 66% decreased movement speed. This is useful in many ways; it can be used to keep incoming foes from reaching the caster, or keep the targets from fleeing the attacks that follow.
In addition to typical damage dealing, Water Magic skills provide a versatile collection of negative effects to throw at the enemy. Water Trident is an extremely useful skill in PvP, as it can knock down moving foes and can be recast shortly thereafter. Maelstrom, on the other hand, interrupts any enemy spells being cast in its area of effect for its duration. Blurred Vision may cause groups of enemies to miss with their attacks.
One of the best aspects of Water Magic is the defensive boost it can give the caster. Armor of Frost, Frigid Armor, and Armor of Mist boost the caster's armor, the latter even increasing his or her movement speed. Mist Form causes the caster to become invulnerable to attacks while Ward Against Harm gives party members in the area of effect a good general armor bonus as well as an additional bonus against fire damage.