According to Jim, its the water product to use cleaning LPs and should be used in all steam cleaning applications. As for # 3 ,I suppose, the correct answer is that commmerical applications also use R/O + water.
As I have noted before, many folks have said that they can not find anything but distilled water in there hometowns. If that is so,than use what you can find and improve when you locate a water upgrade. Should your steaming tank show signs of grime build-up, replace the unit to be on the safe side.