For mountain climbers and people adrift in life boats, this simple inflatable water purifier requires only sunlight and a source of water ideally brine.
Imagine an inflatable rubber ring, approximately 12 across. Now imagine it laying flat, and a thin, black rubber floor across the lower surface
of the ring. Next add a clear dome on the opposite side of the ring possibly with a ring to hang it from a ceiling at the top.
I did an ACSII art of it here, but the editor put it onto one line.
The brine goes on the black floor of the inflatable, possibly through a valve in the bottom. The sun heats it, and causes it to evaporate (thereby loosing the salt held in solution). The water vapour hits the clear dome, and runs down the side where it collects in the v shape between the dome and the ring. During evaporation, any salts will have remained on the black floor of the device.
This would be difficult to clean. I suppose you could let the evaporated water run through it for a while, to clean the sides and the v ridge which collects the waters.
In a rough sea, if used in a life raft, it would be difficult to keep the brine from overflowing into the clean v channel and tainting it, even if the device was suspended from the ceiling.