You could make a fire wizard, or an air wizard easily enough with the cards from the core set, but there's just not enough water or earth to fully focus on those schools... yet.
Still, have to say that the Water School is super important -- it has the "Dissolve" spell, which allows you to get rid of pesky equipment. When we get more water spells in future expansions, you should definitely revisit building a Water-aligned Wizard.