Conditioned tapwater is fine for emergency use in a qt or hospital tank (the WORST aspect of most conditioned tapwater is that the minerals in it don't ever evaporate, and pile up and up and up in repeated topoffs over time---and tapwater can even contain arsenic (in minuscule amounts)) ---Still, if you possibly can, I'd use RODI, because it's got zero content, and the dry salt we use renders it into decent ocean water MINUS the little surprises that the local water supply may provide.