I have several plants & a tree indoors. I live in a place with off-the-scale
hard water, and I only soften the hot side - and then only with potassium,
not sodium. That's all I ever water with during winter. After 24 hrs it's
cooled, dechlorinated, doesn't leave mineral scale, and I don't worry about
upsetting soil pH. Before I moved to a place with a softener I used to melt
snow; and for me it was a far bigger pain in the ass than I was willing to
put up with. Especially for as many plants as I had. Whenever using bottled
water, I always used distilled.

With the exception of some orchids, I almost never fertilize plants indoors,
because that's when I'm enforcing dormancy. When they all go outdoors for
the summer they get an occasional, dilute feeding with stuff like fish
emulsion, or something that I think is made of beets(?).

I've added coffee grounds directly, but that was mostly just to fill in a
couple divots after repotting a Strelitzia.

There are table-top kitchen scrap composters available, too. No odors, so
they claim.