A Wikipedia article on Hydration/Dehydration said that an average person in an average temperate area such as the UK would need 2.5 Liters per day to stay hydrated (that;s about 5 pints, if I've done my arithmetic correctly)..What good is 1 pint a day?
That is for a person doing normal activities like working eight hours a day. For a survivor minimizing his activities he can get along on a lot less water. I have attached a page from the Air Force Survival Manual, AFM 64-5 showing the water needed by survivors in a desert environment and the needs of persons at sea are lower since they can use sea water to wet their clothing to act as artificial sweat.
Looking at the table you can see that temperature is very important in determining water requirements so what was the temperatures that Earhart and Noonan would have been exposed to if in a raft or on Gardner? The air temperature over the ocean is very constant. According to the
U.S. Navy Marine Climatic Atlas of the World. Volume V, South Pacific Ocean (1979) in the area of the Pacific we are concerned with, during the month of July, the temperature stays between 81° F and 84° F for 80% of the time, goes down to 79° F for 10% of the time and all the way up to 86° F for 10% of the time, it never gets any hotter. Of course it might get hotter under the sun back in the brush but not on the sea. You can get similar, but less detailed, weather information from the
pilot chart available here.Look at the table in AFM 64-5 and the line for 80° F and no activity and you find you can last 9 days without any water. You can also see that for every extra quart of water you have you will last another day. So what good is just one pint of water obtained per day? During the nine days you should last without any water your solar still will make 4 1/2 quarts so bringing your survival time up to 13 1/2 days. But in 13 1/2 days the still will make 6 3/4 quarts so you should actually last 15 3/4 days which then makes 7 7/8 quarts so you last 16 7/8 days but then you run out of time so one pint a day adds about 8 days to your survival at 80° F
in the desert. Something else you can get from this table is that with one quart a day you can last indefinitely so two stills should keep you alive forever
in the desert. The caption under the table points out that it takes two to three times as much water to survive
in the desert than it does in other environments, so on a sea shore or at sea a person could survive on only one-half to one-third of the amounts of water listed in this table. On the TV show "I shouldn't be alive," one of the shows was about a guy who survived 76 days, in life raft, all by himself, drifted all the way across the Atlantic and made landfall in the Lesser Antilles. He was hungry and thirsty, he lost a lot of weight, but he was still alive. He had started with three WW2 surplus solar stills but he couldn't figure out how to get them to work so he sacrificed one of them by cutting it open to discover how it worked. He then got enough water from the remaining two stills to last him for 76 days and he was still husbanding a few pints of his sealed emergency water cans when he reached land.
I have also attached a page from the British Special Air Squadron (the SAS) Survival Manual showing similar information for survivors at sea. According to this manual you can actually survive on even less water, 2 to 8 ounces per day depending on temperature, and 8 ounces is only one-half of a pint.
So the solar stills developed during WW2 would be able to supply sufficient water to keep people alive for a long time and possibly indefinitely.
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