Problem is, to short circuit a wizard using water, you would have to have a constant stream running over him, like Nick did in DM. Other than that, most you would likely accomplish is him not being able to cast for an exchange or 2, so a block against his discipline would probably be the way to go. As long as he can't overcome the block he won't be able to cast any spells. Sort of like an entropy cloud around him that keeps him from shaping a spell.
Or, as you pointed out, you can do it as a maneuver.
Another way to do this would be through thaumaturgy, like Harry did to Kravos in GP. He had a doll with some of Kravos Hair and he used it to block out his spellcasting for the entire scene. Would also be a block against his discipline (or maybe even conviction?) I think, but with a hell of a lot more oomph than you could accomplish with evocation. Plus it will last a hell of a lot longer than an evocation would.
And of course there is the simple "draw a circle, add a drop of blood" trick. Kincaid used it on Harry once, but I have no idea how one would do that in terms of the rules. Plus, the circle is easily broken. Still, even mortals can do this.