You can make virtually any water source potable by boiling it. It so happens hot water has other useful purposes as well so why are we not showing those 1.8B people how to efficiently boil water? What am I not getting?
If you're boiling in some sort of still, sure, that will remove impurities, but those aren't common household items. Boiling a pot over a heat source will only kill bacteria; it won't remove impurities.
I would wager everyone out there knows, either explicitly or implicitly, that boiling water is a great way to clean it. People are looking for something better that can scale to give everyone clean drinking water. Boiling water for the length of time needed to render it safe to drink is terribly energy-inefficient, which is why it's not done in water treatment plants anywhere in the developed world.