"A little osmosis machine"... Where do I find these? Would it fit in my appartement? Can I install it without plumbing if I am only a renter? How often do I need to clean it? How often do I need to change the filter? How many kW and how many liters of wasted water do I need to spend to get half a liter of osmosed water?

Your recommendation may be valid for large volumes long term (like the aquarium or brewing at craft beer scale), but for all the other uses not.

You can get no install ones that go on your counter or light install ones you connect under your sink (no more difficult than installing a bidet in your apartment). Cost wise they are cheap enough they pay for themselves (including filters) vs even cheap bottled water over the course of a year (well, if you only drink 1 bottle per week or something the economics will be different - 2 bottles per day should ~break even). ~3 filters per year, depends on the model and usage.

Bottled water is usually just a convenience factor of "I can take x bottles from this pack wherever at once on demand, or even grab them full of water I like while not at home".