Natural fibers possess an inherent affinity for water, which significantly influences their physicochemical properties and interactions with other substances. Polymer adsorption on natural fibers is a critical process, relevant to areas ranging from plant cell wall formation to applications like papermaking, energy storage, and biosensors. Numerous studies have suggested that polymer adsorption on cellulose surfaces is driven by hydrogen bonding. However, current understanding suggests that polymer adsorption on hydrated systems such as cellulose is primarily driven by the entropy gain resulting from the release of structured water molecules.1The primary objective of this study is to further elucidate the role of interfacial water in the polymer adsorption on natural fibers. Water molecules exhibit a strong dipole moment, and thus, the presence of surface charges leads to a preferential orientation of water molecules near the interface.2 This alignment of water molecules is determined by the nature and density of the surface charges. A positive charge typically aligns the water dipole such that the bisector of the two OH bonds is oriented towards the charge, whereas a negative charge acts as an H-bond acceptor, aligning the hydrogen atoms towards it.We have developed a model system using zwitterionic nanofibrils, where the dominant surface charge can be adjusted by varying the pH, consequently altering the structure of the interfacial water. Non-ionic polymer adsorption experiments, conducted using a quartz crystal microbalance with dissipation monitoring (QCM-D), highlighted the crucial role of interfacial water in the polymer adsorption process. Our findings underscore the importance of interfacial water in the adsorption dynamics, providing deeper insight into the interactions between polymers and natural fibers.