[Arodex]

"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.

[TrueSlacker0]

Its a reverse osmosis machine. You can get them for as low as $100 on amazon or anywhere. I have one at the house attached to my sink that makes about 20 gallons a day on demand and a small commercial one at work that cost 220 and makes 500 gallons a day (its about 2sqft in size) filling a large tank. Neither are large nor high in electric usage, the home one has no power, the small commercial has a small booster pump. Its the water usage that is high, to get a gallon of pure ro water is about 1.5 to 2.5 gallons of "waste". You can use that waste for watering the lawn or rinsing things but its extremely mineral heavy. You dont clean them just replace the filters every so often (not nearly needed as often as recommended)

[HWR_14]

Is the waste higher in the unpowered machine than the powered machine? Because saving electricity at the cost of water isn't necessarily a good thing .

[saltcured]

The inherent issue with reverse osmosis is that you build up a "brine" on the input side. And the higher the gradient of these ions, the harder it is to do to the reverse move. The normal osmotic action is to pull pure water back through to dilute the brine.

I've heard of systems that attempt to just let the brine diffuse back through the source water system rather than dumping it. But, I think this is against code in any modern, thoughtful regulatory environment. You normally want explicit back-flow prevention to reduce the chance of contamination of the water system by end users.

[amluto]

You can also get gadgets called “permeate pumps” that consume no electricity and help a bit.

[zamadatix]

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".