In space resources are limited.  I’ve had a chance through friends who work at NASA to explore the Houston mock-up of the ISS.  It’s surprisingly large, but imagine having to keep everything a group of people might need for months.  There’s no easy trips to Target here folks.  That’s where 3D printing comes in where simple filament could be turned into almost anything.  However, wouldn’t it be cool if the filament could be made from waste so not even that took-up space?  The video does a great job explaining how urine is “mined” in space and how the urea being a carbon source could potentially be converted to filament through a yeast intermediate.  Gotta get over the mental parts I’m sure of drinking urine and perhaps brushing with a former urea toothbrush, but every drop of water in our world was somewhere else once, we just like to live in blissful ignorance of where that might have been.