“Total body water was determined by deuterium oxide dilution in 17 normal male subjects with a range of 55.9% to 70.2% and an average value of 61.8% of body weight. Eleven normal females ranged from 45.6% to 59.9% with an average of 51.9%, or 9.9% less than the males. These total body water figures have a precision of ± 800 cc. or ± 2% of total body water in a normal adult.”
That’s a quote from the study “The Measurement of Total Body Water in the Human Subject by Deuterium Oxide Dilution: With a Consideration of the Dynamics of Deuterium Distribution” (by Paul R. Schloerb, Bent J. Friis-Hansen, Isidore S. Edelman, A.K. Solomon, and Francis D. Moore, published in The Journal of Clinical Investigation, vol. 29, no. 10, 1950, pp. 1296-1310), perused in the article “Water in Bodies” in the special WATER issue (vol. 29, no. 2) of the magazine.