Crystalline interfacial water layers have been observed at room temperature on both hydrophobic and hydrophilic surfaces -in air and subaquatically. Their implication in biology (and evolution) was postulated in a visionary paper in 1971 by Szent Györgyi. Today, they are believed to play a fundamental role in protein folding. A recent X-ray diffraction study reports on their presence on crystals in contact with their growth solution. Their subaquatic persistence on hydrophobic solids was reported in 2007. Their relevance in nanoscale phenomena is reflected by the multidisciplinary focus in their study. In the course of a systematic exploration of interfacial water layers on solids we discovered microtornadoes, found a complementary explanation to the surface conductivity on hydrogenated diamond, and arrived at a practical method to repair elastin degeneration using light. The result was rejuvenated skin, reduced wrinkle levels, juvenile complexion, and lasting resilience.Conforming to an extreme sensibility of interfacial water layers to direct observation techniques, a major part of the existing data stems from computer models. Experimentally, interfacial water layers have been studied by X-rays and neutron scattering, 1,2 atomic force microscopy (AFM), 3-5 near-field scanning optical microscopy (NSOM), 6 atomic force acoustic microscopy (AFAM), 7 drop evaporation experiments, 8 and recently on hydrogen-terminated nanocrystalline diamond. 9 A synoptic analysis of all these perspectives provides an increasingly clear picture of the nature of interfacial water: The central and probably generalizable result seems to be that the structural difference between water layers on a solid surface exposed to air, and water layers that prevail at the interface between the same solid surface and bulk water, is less pronounced than that between water layers on a hydrophobic and a hydrophilic surface, studied under identical conditions. The practical importance of this insight is enormous: Extracting information on water structures in air is simpler than probing water layers at the interface between a solid and bulk water, and we are justified to use the structural information (molecular order, density, or viscosity of the water) acquired in simple systems for modeling complex systems. In practice, this means that structural information obtained for instance by AFM in air on a certain model substrate could be transferred for modeling partial aspects in biological systems. The relevance of the "partial aspect" approach becomes clear from realizing that biological surfaces are inhomogeneous: Their dynamic nature, with nanoscopic patches varying in polarity and topography, exclude a macroscopic perspective and complicate distinctive experimental insight. Thus, the requirement for model surfaces, which permit us to mimic specific biosystem aspects, is clear. Obviously, biocompatible materials based model surfaces are the best choice here. The themes investigated have one aspect in common: The substrates impose their orde...