I think I need to be more long form because people are getting the wrong idea. Desalination from seawater is almost never required, brackish sources are more common. For this multistage flash distillation is the cheapest option, reverse osmosis next. Even then most people could recycle grey water rather than run desalination. A sand filter works for this. These types of gizmo based approaches just strike me as incredibly naive as to the underlying causes of problems with water supply. More than naive, patronising. People in poor countries aren't stupid.