Water is conventionally viewed as a disruptive solvent for supramolecular materials, destabilizing directional noncovalent interactions. Here, we report a metal–organic material in which water instead acts as a structural co-monomer driving the formation of supramolecular fibers. A zinc(II) bisphenoxyimine (“Salphen”) complex featuring convergent hydrogen-bond acceptor sites assembles in bulk water into long, hollow nanofibers stabilized by confined structural water molecules. Single-particle analysis and density functional theory reveal tubular architectures in which intercalated water bridges the metal centers and defines a hydrophilic inner channel. The fibers form hydrogels with thermomechanical response, chemically triggerable disassembly and enable selective chiral recognition of amino acids via water-mediated molecular–to–supramolecular information transfer. In organic solvents, the water content can be used for control over supramolecular self-assembly and hence gelation and liquefaction. Our findings establish structural water as a design element for creating adaptive, chiral, and dynamically reconfigurable metal–organic materials, offering a new paradigm to unlock this sustainable building block in supramolecular materials design.