I don’t believe you can figure out the water content of a living human. And if you can, I don’t want to know how.
You could just weigh a mummified body instead, figure out how much a living person of the same sex and height would weigh, and the difference would be water. (Not accounting for the internal organs that were removed during mummification).
People have said the fact is derived from experiment done on live human subjects by the WW2 Japanese torture unit, Unit 731.
I don’t believe you can figure out the water content of a living human. And if you can, I don’t want to know how.
You could just weigh a mummified body instead, figure out how much a living person of the same sex and height would weigh, and the difference would be water. (Not accounting for the internal organs that were removed during mummification).
Same way you learn the water content of any vegetable. Weigh it, then stick it in a kiln at 100 degrees for a few weeks, then weigh it again.
Somewhere there’s some catacombs with dessicated corpses. I think it might have been Prague. So you could weigh some of them and take an average.
For anyone not aware of them, there’s a rather intense set of Behind the Bastards podcast about it.
Truly grim.