Sorry to be a stickler for linguistics, but "thinking" something is a human right or not doesn't make it, or not make it, a human right.
The question you asked in your title "is water a human right?" and the question you seem to be asking in your post "should water be a human right?" mean two completely different things.
Anyways. To answer the question in your title, it seems sensible interpret Article 25, part 1, (of "the list of human rights") as including safe clean water.
(1) Everyone has the right to a standard of living adequate for the health and well-being of himself and of his family, including food, clothing, housing and medical care and necessary social services, and the right to security in the event of unemployment, sickness, disability, widowhood, old age or other lack of livelihood in circumstances beyond his control.
So is it a human right? Yes it is.