How have you been keeping cool this summer? Did you go to your local pool or take a trip to the ocean? I hope you didn't try drinking ocean water. Salt water has no thirst-quenching benefits. It depletes body fluids, causes muscle cramps and dry mouth and can lead to severe dehydration. Imagine being a sailor stuck at sea without freshwater where there is water everywhere but none to drink.
Modern cruise ships, submarines and ships of war can easily make their own fresh water, but that technology was not developed until the 1960s. When Carnegie Science Center's USS Requin sailed the seas in the 1950s, sailors had to make their own fresh water from salty sea water through a process called distillation. Salt water collected from the ocean was put into large tanks and boiled. When water boils, it evaporates into steam. The steam was collected in another part of the tank, and as it cooled down it re-condensed into fresh drinking water.
Sailors needed a plentiful supply of freshwater while at sea, especially those who served on submarines. Submarines had four huge engines that made most of the vessel 100 degrees or hotter. Because the distillation tanks could make only 60 gallons of water an hour and could operate only when the submarine was on the surface, sailors had to ration their fresh water to make it last.
Besides being used for cooking and drinking, fresh water's most important use was to keep the batteries that ran the submarine from overheating. If the batteries overheated they would explode. Because salty ocean water would short out the batteries, it couldn't be used to keep them cool. Fresh water's least important use was for taking showers. Submarine sailors took only one shower every 10 days, using only five gallons of water. These showers lasted 30 seconds and were timed by someone with a stopwatch.