I've just rewatched the second episode of season 3, and Walter's obsession with contamination was already there when he picked the bandaid that was soiling the water of his hotel's swimming pool!

His "I can't be the bad man" said a lot about the show's boldness, given that Walter, with the passing of time, is turning into(or is revealed as) a bad man while he is the lead, which goes against the usual tv formula. Breaking Bad broke the rules.