I was wondering about this because that seems like a good idea upfront, but apparently:
- The extra minerals and stuff is a very minor benefit for plants and will not substitute for fertilizer.
- If you put salt or seasoning in the boiling water, don't use it for plants.
- The starch might also promote mold / bacteria growth.
Trisquel provides a good experience out of the box imo, as long as your hardware is supported and if you don't mind the dated looking interface. I used it for a while on my corebooted laptop.
I didn't used much any other "100% libre" distros. As much as I wanted to use it, I never managed to have Guix to run on that machine.
[edit:] to answer OP's question, I would use a distro that ships with it.