Water Scholars/SensePoison

Would allow a water scholar to see a green aura around tainted objects (food, weapons, etc.) This would be a far better alternative to casting "cleanse food" on every piece of bread that comes your way.

Alternately, you could expand this to a "Sense danger" type of thing, so you could see wards of fire and what not. But that seems like it might fall under the purvey of spirit stuff. Go figure.