Due to its high specific surface area and abundant surface polar groups (such as hydroxyl, carboxyl, and other ionic functional groups), nanocellulose exhibits strong interactions with water. The presence of water in nanocellulose can introduce diverse functionalities, serving multiple roles. In this presentation, I will discuss our work on leveraging water to tune the mechanical properties of nanocellulose-based products, enhance processability, and enable functionalities such as sensing and actuation. Water-induced hydrogen bonding can transform wood into a strong and tough structural material, with water molecules actively participating as structural components through hydrogen bonding. Additionally, water can plasticize nanocellulose, converting 3D-printed nanocellulose monoliths into elastic structures. Furthermore, I will demonstrate how the interaction of water with TEMPO-oxidized cellulose nanofibrils can transform CNF films into both humidity sensors and moisture-induced actuators. Therefore, this presentation highlights the importance of water-nanocellulose interactions in the development of high-performance functional bioproducts.