# Desalinization of seawater by stone? **URL:** \ **Category:** Factual Questions\ **Created:** [October 1, 2012, 12:50am UTC](https://boards.straightdope.com/t/desalinization-of-seawater-by-stone/636344 "2012-10-01T00:50:06Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [October 1, 2012, 12:50am UTC](https://boards.straightdope.com/t/desalinization-of-seawater-by-stone/636344/1 "2012-10-01T00:50:06Z")
I took a tour of the [Mission Houses Museum](http://www.missionhouses.org) 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. ---
**Author:** ![sitchensis](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sitchensis/32/4892_2.png) [@sitchensis](https://boards.straightdope.com/u/sitchensis)\ **Post date:** [October 1, 2012, 1:32am UTC](https://boards.straightdope.com/t/desalinization-of-seawater-by-stone/636344/2 "2012-10-01T01:32:31Z")
Are you sure it wasn’t a [salt making system](http://www.donch.com/lulh/nhh1.htm)? As in pour saltwater in stone basins and let the water evaporate away leaving the salt? > [@](#): > > Salt was an important article among the Hawaiians and they were adept in the manufacture of a coarse salt from the sea water. Two methods were employed: One, that of putting the water in shallow scooped-out stone dishes to evaporate; the other, by impounding the sea water in small shallow ponds and collecting the residue as the water evaporated. Salt Lake, on Oahu, also was an important source of supply. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [October 1, 2012, 1:36am UTC](https://boards.straightdope.com/t/desalinization-of-seawater-by-stone/636344/3 "2012-10-01T01:36:41Z")
Well, the docent clearly said it was for removing salt, but that doesn’t mean she wasn’t confused. Oh, and one thing I forgot to mention - these were apparently typically used on ships, and were from a ship. ---
**Author:** ![the\_diego](https://avatars.discourse-cdn.com/v4/letter/t/7bcc69/32.png) [@the\_diego](https://boards.straightdope.com/u/the_diego)\ **Post date:** [October 1, 2012, 9:45am UTC](https://boards.straightdope.com/t/desalinization-of-seawater-by-stone/636344/4 "2012-10-01T09:45:04Z")
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. ---
**Author:** ![Heracles](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/heracles/32/487_2.png) [@Heracles](https://boards.straightdope.com/u/Heracles)\ **Post date:** [October 1, 2012, 11:01am UTC](https://boards.straightdope.com/t/desalinization-of-seawater-by-stone/636344/5 "2012-10-01T11:01:43Z")
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. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [October 1, 2012, 12:02pm UTC](https://boards.straightdope.com/t/desalinization-of-seawater-by-stone/636344/6 "2012-10-01T12:02:55Z")
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. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [October 1, 2012, 12:36pm UTC](https://boards.straightdope.com/t/desalinization-of-seawater-by-stone/636344/7 "2012-10-01T12:36:31Z")
> [@beowulff](#): > > Well, the docent clearly said it was for removing salt, but that doesn’t mean she wasn’t confused. > > Oh, and one thing I forgot to mention - these were apparently typically used on ships, and were from a ship. That could still be the function, removing the salt from the water. It’s just that the salt would be left over instead of the water. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [October 1, 2012, 1:38pm UTC](https://boards.straightdope.com/t/desalinization-of-seawater-by-stone/636344/8 "2012-10-01T13:38:01Z")
Doubt it was sandstone, if they were native rocks.