I don't know if this is a good substitute for Nuun tablets in terms of ingredients, but I think Skratch Labs sells a powder to add to water. Might be worth looking into.
(Come to think of it, I think I bought a single-serving thing last year and never tried it. I guess I should look for it when I get home...)
- Gray 2010 carbon WSD road bike, Rivet Independence saddle
- Red hardtail 26" aluminum mountain bike, Bontrager Evoke WSD saddle
- Royal blue 2018 aluminum gravel bike, Rivet Pearl saddle
Gone but not forgotten:
- Silver 2003 aluminum road bike
- Two awesome worn out Juliana saddles