Solarpunk technology

I first thought about posting this in [email protected], but then I remembered that salt removal is not only beneficial in hydro gardening, but also done worldwide to get access to drinking water. To survive.

I'm mainly looking for ways to get pure water (without, or at least with less than before, dissolved salts), because the tap water is very hard where I live.
But, I think most methods that remove "my" salts (around 300 ppm of stuff like calcium, carbonates, etc.) could also remove salt from sea water to make it drinkable.

Right now, I can think of those few options:

• Reverse Osmosis: this is the method I currently use, and which is also industrially used everywhere, including sea water purification. It's pretty great.

Problem: a big part is very salty waste water, which is usually pumped right back into the sea, which creates oversalty dead zones, or, in my case, over 5 parts "waste" water per 1 part pure water.

I have a hard time using all this (still clean and perfectly usable) water. Currently, I just flush my toilet with it, but it's still kinda annoying.

• Rainwater collection: not technically salt removal, but more of a way to get already pure water. I do that in summer, but now, in winter, that's not feasible. Also, there's dirt in it.

• Distillation: extremely energy intensive on larger scales, and with smaller passive ways (e.g. foil tents that collect condensates) it's very ineffective.

• Boiling it: I do that too sometimes. Boiling removes carbonates, and makes some minerals precipitate out of solution. But that isn't proper salt removal, it's just better than nothing for me.

• Freezing it: in the lab, many chemicals are recrystallized after synthesis to purify them, because molecules like to link to each other, and then "push out" any impurities from the crystals. If I just take a bucket of tap water, put it out overnight at negative degrees, and then melt the ice crust above, is the surface ice theoretically pure water?

What other ideas do you have?