See attached. Trans Epidermal Water Loss (TEWL) is said to and can occur when the loss is 10% ( +/ - ) within the SC but that is just the research I have done. See the details on what I researched on the diagram as far as the water content of the skin.
Also, this part is not understood till today:
The Enzyme which controls de squamation must have a specific amount of water and that is really the biggest issue here. When it drops the process stops and that is where the Dry Skin Cycle starts and the real problems occurr.
I would like to add that I have never needed this information for a client but agree its good to at least have knowledge of. Hope this helps.