Abstract: An elongated flexible housing has an upper part which is water-tight and communicates with a lower part which is formed with a semipermeable membrane for passing through by osmosis pure water components out of sea water. The semipermeable membrane is covered with a fabric having a mesh size between 0.05 and 0.5 mm, to assist in the retention of salt. The waterproof housing part is foldable over the other part, including the membrane, and is filled with a highly concentrated solution of fructose or with glycine. The folded parts are enclosed in a snugly fitting protective envelope of a waterproof material. In a modification, the two housing parts are disconnectably attached to each other by means of a screw nipple.