What do rocket scientists have to do with designing water purification systems? On the assumption that you may not be a native speaker of English, I'll mention

What do rocket scientists have to do with designing water purification systems? On the assumption that you may not be a native speaker of English, I'll mention that here in the United States, at least, the term "rocket scientist" (which some people who work on the International Space Station project literally are) is a synonym for "very smart person." In other words, my statement is that even though the International Space Station presumably has enough prestige and budget as a project to hire very capable engineers, those engineers have not found it easy to design a toilet-to-tap water treatment system (as the linked article in my first comment reports). Yes, designing a system to work in free fall while confined to the space station is itself a difficult engineering problem, but even here on earth in normal-g conditions, it looks like there is a lot of engineering work still to do on the problem of potable water recycling.