Translation:We can drink that water without any risk.
Interesting comment. I always learnt that "on" is the impersonal or general form of the second person singular - translated in English as "one" though not widely used in English (more commonly translated as the general "you"). So what you are saying is a shift in common usage in French - the old language constantly changing argument.
Did you put "with any risk" or "without any risk"
The French sentence says "sans aucun risque"
"Sans" = without". Therefore the literal translation is "we can drink that water without any risk". This seems a perfectly good English sentence but DL has also accepted the equivalent "with no risk". This of course means the same thing but loses the direct link with "sans".
If you put "with any risk" then your sentence is wrong as it does not make sense.
If you put "without any risk" and so you are asking about the translation of "on" as "one" - your answer was correct. This sentence could translate as "one can drink this water without any risk"