Schmidt-Nielsen points out that the oxygen consumption must  be taken into account, since the more oxygen required for a specific 'fuel', the more water is lost

from the lungs. He calculates that, for a gain of 10,000 kcal,

oxidation water for fat is 1.13 kg, whereas water lost in

respiration is 1.8 kg (a net loss of 0.67 kg).

This mean that  fat oxidation in the hump as a source of metabolic water may rather leads to water loss and deficit.