This is absolutely and definitively FALSE. According to Aristotle's "history" in Metaphysics Alpha, Thales was the PreSocratic philosopher who believed that the fundamental principle (arche) of everything and the ultimate matter out of which every natural object is ultimately constituted is water. But Aristotle categorically rejects this. In his conception of nature matter is always relative to form (with one possible exception); it is potentially an informed object, and different forms (depending upon how complex they are) require different types of matter. For example, bronze is the matter for a statue; it is that which, when a sculptor imposes a certain form on it, becomes an actual statue. For Aristotle the body is the matter of the soul; it is that which is capable of being an instrument for the soul's various life-manifesting activities. Now, there's scholarly debate about whether or not Aristotle ultimately posited a kind of "prime matter" to explain and render intelligible the inter-transformation of the elements. Whether or not he did, he definitely didn't think that all matter is made up only of water.
