Many years ago I heard a lecture from Rav Hershel Shachter on kashrus. In the course of that lecture, he explained that even water needs to be researched. He said that treif liquids can be (and sometimes are) run on the same lines used to bottle water. To be honest, I had never thought until then to check if water has a hechsher. It seems to me it is really not so simple to pasken by ingredients.
