I do not think that I lost more fat in the DF vs the WF. After the DF I gained 5 pounds just drinking fluids whereas in the WF the weight I regained was a combination of rehydration and refeeding.
I think in WF I actually burned more fat based on ketosis scores. I remember that in my first DF I was in heavy ketosis on the WF when I began the DF and my body after a day or two reverted to moderate ketosis - probably as a protective measure.
Also, I do not think the body burns fat to get water during the DF because the DF is not long enough. The body has a lot of cellular and inter-cellular water that it uses first. One would have to do a really long DF to get to the stage where the body conserves it excretions and that stage is probably too dangerous since it would mean no urine eliminations.