Debye’s theory of water dielectrics is truly remarkable, especially given that he had no knowledge of the nanoscale structure of water. His crucial assumption that water polarization aligns with the internal electrostatic field paved the way for major progress and magically simplified the electrostatic theory. Debye never meant his theory to apply in contexts where water polarization may result from physical constraints operative at nanoscales. That was not even in the cards in the late 1920’s.
After being mislead for decades by researchers that kept on invoking effective permittivity constants and other extrapolations from Debye’s ansatz, I finally came to grips with the fact that Debye’s assumption breaks down for biological water. This observation, simple as it is, may herald the advent of a new chapter in molecular biophysics. Time will tell of course whether we are truly at the gates of a paradigm shift, but for now you may find more on this thorny subject at
Ariel Fernandez (2013): Breakdown of the Debye Ansatz at Protein-Water Interfaces. Journal of Chemical Physics 138, 225103.