Comment I wonder how much the water in the air factors in (Score 3, Interesting) 133
Having lived in very dry places. (It frequently gets below 5% humidity in the summer outdoors) I know that with low humidity you can dry out fairly quickly. In Phoenix you are allowed to carry water into most sporting events because you need to replace the water that evaporates and everyone does it in the summer.
When you are in someplace that is humid, you do not dry out as quickly because the water is being replaced by water in the air (yet I know there are other factors),
It would be interesting to strictly control the isotope content in diet/drink for a month but in two different regions and then do a comparison.