You alter a drink as soon as someone drinks from it, turning water or water-based beverages into poison. Failure results in poisoning and possible weakening of their fortitude, with effects persisting until they succeed or the spell ends.
You gesture, and the liquid in the cup darkens, swirling with toxic hues. As someone takes a sip, the beverage bubbles ominously, transforming into a venomous concoction that poisons them upon ingestion.