I took a tour of the Mission Houses Museum in Honolulu recently, and one of the object they had on display was described by the docent as a seawater desalinization system. It consisted of two large stones (maybe sandstone) that had been hollowed out and were suspended over a catch bucket. Presumably, one poured saltwater in the hollows, and caught the freshwater in the buckets.
I have a hard time believing that such a thing could work, unless the stones were some sort of material that could trap sodium ions. Has anyone ever heard of such a thing? Is it even possible? I suspect that this was a water filter, and the function has been mis-remembered over the years.
if you are somehow able to precipitate salt, then the water comes out less salty than seawater. maybe it’s possible to a certain extent using a porous medium but will not entirely remove it.
Perhaps some parts were missing. There are modern systems that use a container of saltwater (the stones?) that’s painted black and gets heated in the sun, and a membrane suspended above it that collects the resulting condensation and makes it fall into a second container. I guess this could also work if there’s a way to heat the stones directly instead of using the sun.
If it was a filtration system (I don’t believe it can be, for technical reasons anyway), the stone would quite soon become saturated with salt and would need replacement - carving a new stone bowl for maybe a couple of week’s supply of water seems like a losing proposition.