Just boiling it should suffice, but you'd need quite a lot. My dear departed mother tried a "slimming aid" in the 1970s which consisted of a plastic bag that you could wear, the result was intense sweating, dehydration and a weight-loss that was reversed as soon as you drank some water. Maybe something like that?

But why?

Extracting is easy, just wait and evaporating, but collecting would be an inefficient process because of scale and topology of surfaces

Why?