Lately I have seen a number of unrelated "scientific" debates over whether certain substances should be outlawed because they are toxic to humans. My initial, informal reaction is usually to respond that anything is toxic to humans if you give them a sufficiently large dose.
However, formally I don't know if that's really true for everything a human being could ingest in some way. I started to wonder if there were some substances that our body could handle unlimited amounts of without any negative consequences.
As this question has been (correctly) identified as a bit vague, I'll try to explain what i'm looking for. For the purposes of this question, I'm willing to ignore the limitations of actually ingesting a given substance in "the usual way". For example, if you can't physically drink enough of some liquid fast enough to kill you without your stomach filling up and vomiting, but that same liquid injected intravenously could be lethal, I could consider that toxic. I also recognize that the body can only physically contain a certain volume of stuff, after which sheer pressure would cause it to fail; I'm more interested in "biochemical toxicity" as opposed to any physical damage (I just don't know the term for what I'm looking for.)
In other words, one of my goals is to learn if, under laboratory conditions, a properly motivated researcher could always find a dose that would be toxic, regardless of the impracticality of a real person ingesting that dose under normal circumstances.
So, with that qualification, my ultimate question is:
Is there any substance we know of that is completely non-toxic to humans at arbitrarily large doses ingested over an arbitrarily short period of time?