Dr of BBQ
Call your local health department because the answer will eventually have to come from them. Although I have never heard of that rule before.
Recently on my step van build I called my HD and asked if a mop sink could double as a hand washing sink and they said ok.
Then 1 month later they said a hand sink can ONLY BE USED TO WASH HANDS!
But when I told them, or reminded them, about our phone conversation they said ok.