I was wondering how the total amount of water in a typical human varies by weight and sex. I saw a site claiming that the typical male/female water percentages by mass were 62% for men and 51% for women; fair enough, though I've seen higher figures. (I'm more concerned with the ratio between the two than the absolute level, in both cases.) It also says (understandably) that the water percentage decreases as BMI rises. The particular figures it gives, though, are hard for me to swallow. Consider a range of people with identical height (or a single person gaining or losing weight), so that their weights are proportional to their BMI. At the obesity threshold, the water weight would be 30 * 48% = 14.4 units; at the morbidly obese theshold, the water weight would be 40 * 36% = 14.4 units. That would suggest that gaining weight (at least past a certain point) does not increase the amount of water in the body, which seems questionable to me. Does anyone have better figures? Or know of a database that records appropriate information to determine the answer?