I don't have the scientific facts to explain but really I think it has to do with the interaction in the endocrine system. Even excess progesterone will convert to estrogen,but it is not called aromatization . I think discussing things in absolutes is misleading. It is like saying relatively speaking anavar is mild on the liver.... well, it still causes stress to the liver and given underlying conditions a little bit of stress can be a big problem for some people. So back to the water retention, what else causes water retention? If all else is equal you have to look at the var and say there must be some aromatization. I could be totally wrong but I don't have any scientific experiments to help me out either.