We can go with Reverse Osmosis systems which will do fine. I have nothing against them other than when all hell breaks loose and you cant get replacement membranes. I will have an RO before it is all said and done. The amount of drinking water to be made with little effort is appealing.

Option two. The homesteaders solution. I plan on building a solar still and then to expand its production use an open flame gaslight fueled by my biogas. This set under a piece of copper pipe fed from the still and discharge a little higher around the water level would give enough water vapor to have the still produce at night also. This will give me a good dependable supply of distilled water and also battery water. At roughly $2 a gallon here and the need of weekly filling of batteries it could add up.

Now total survival mode when everything falls to crap or you need to get some major water made under less than ideal conditions.

I figure I can get a 1hp steam engine and hook it up to a 12v alternator. This would allow a charge that would run some lights and a fan or two.

If I used a mono tube boiler with scrap wood as a fuel source I could use sea water or other surface water and produce about 5 gallons of water an hour with a condenser on the discharge side of the engine.

I could put this in the back of a pick up truck and send it down the road to family if something happened where they had the need. Basically every hour this operates would keep ten people alive for a day. I am guessing around 2k investment when all said and done.