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NASA is recycling 98 percent of astronaut pee and sweat on the ISS into drinkable water
(www.engadget.com)
This is a most excellent place for technology news and articles.
You're not far off, most spacecraft have multiple parts, you can simplify to two:
the orbital module and the return module
The Dragon does indeed have an expendable module they call the "trunk". The capsule comes home but the trunk doesn't.
The NG Cygnus, ESA ATV, and JAXA HTV are all fully expendable. They burn up completely.
The soyuz is the best example, it has three parts and only one comes home. They save a lot of weight by only needing to make one part strong enough to make it back.
Picture from Wikipedia:
https://en.m.wikipedia.org/wiki/File:Soyuz-TMA_descent_module.jpg