Sign to warn tourist about water

I would go for untested water. The term water testing exists. The Planet Magazine has a post about it which says:

Before you stoop for a drink at Western’s untested water fountains, ask yourself, is it really worth it?

It has this picture with a detailed notice, saying:

Water testing results pending mitigation completion. Please use other sources for drinking until further notice.

If there is a risk, it is better to be explicit about it, rather than concise.

You could also say water not tested, though sometimes this expression requires a continuation (for lead, by a laboratory, etc.)

Only 2. and 4. are incorrect or unidiomatic. ("Untested" or "uncontrolled" would be more correct.)

However I don't think any of the choices given are a good under these circumstances.

Vaguely describing the status of "control" or "testing" is far too indirect an approach for communicating a safety concern. What would you be testing or controlling for anyway, temperature? pressure? I know you're talking about pathogens or chemical contaminants, but I work for an engineering firm that builds water treatment plants. I wouldn't expect that knowledge from the general public.

I would say: "Water may contain organisms that can cause disease." or "Water may contain arsenic which may cause poisoning." or something like that. Then follow up with "Drink at your own risk."