User blog comment:Njalm2/Nanja's Grimoire: Evocation/@comment-18812574-20151231164504/@comment-3403804-20151231172251

Evocation deals with insubstantial energy, any spell that would produce water would be a spell of Conjuration, not Evocation. Conjuration deals with creating something from nothing, whereas Evocation is akin to issuing forth raw energy in it's primal state, Hadou is typically a blend of Conjuration and Evocation. Although the true spells of Conjuration are typically much higher ranked as they're more difficult overall. Kurohitsugi for instance, is a Conjuration spell.

Evocation is limited to raw energy, this is what allows a Wizard to produce the result as opposed to the actual process. Each School can in some ways be seen as a category of magic with their own criteria.