From Legislative History: Saline Water Conversion Act
During World War II, the castaway problem reached such proportions that the military initiated several projects to find ways for providing emergency supplies of water. Once solution to the problem was the desalinating kit using de-ionizing chemicals. These kits produced by the Permuti Co. utilized a briquet composed of silver zeolite and silver oxide; when added to sea water in a plastic bag, the crushed briquet removed sodium, calcium, magnesium, and chloride ions as an insoluble precipitate.
This paper DESALTING SEA WATER..
. . .
A Practical Chemical Method has extensive details and shows this (poorly reproduced) image of how the system is used.
It is captioned
The picture at the top shows a briquet of desalting chemical. Next the
briquet is dropped into the plastic desalting bag filled with sea
water to the marked line. In the third photo the hard briquet disrupts
spontaneously, and water and chemical are thoroughly mixed by
kneading. After about an hour clean water is sucked through the
filter at the bottom of the bag.
The complete instructions are given as:
The operation of the kit is best indicated by the directions printed
on on the desalting bag:
Screw plug firmly into outlet tube of this bag.
Fill bag to filling line with sea water.
Pull off one package of chemical from tape. Follow directions on wrapper. (The directions on the wrapper of the desalting briquets read as follows: Use only one at a time. To remove
foil, cut end of wrapper on edge of can. Tear off foil, then cut
end of inner cellophane wrapper on edge of can and pour entire
contents into bag of sea water.)
Then fold top of bag down tightly and roll toward buckle.
Chemical breaks up in a few minutes. Further pulverize
it by kneading gently for 10 minutes.
Shake bag gently for an hour. Water is then ready to
drink when filtered.
To filter water, first unscrew plug from outlet tube. Then
gently squeeze bag or suck on tube. Spit out first few drops only
if they are too salty.
Replace screw plug. Water may be left in bag with chemicals until wanted.
When all water is drawn from bag, rinse out chemical
with sea water.
The paper also contains extensive discussions of the chemistry involved. Chemistry is not my forte but if I am interpreting the paper correctly (a stretch, admittedly), these are the reaction equations involved.