In the title compound, C(13)H(13)N(5)O(4) x H(2)O (4,5'-cyclowyosine x H(2)O), the cyclization forces a syn arrangement of the aglycon with respect to the sugar moiety. The ribofuranose part of the molecule displays a beta-D configuration with an envelope C1'-endo pucker. The molecules are arranged in columns along the short a axis and are linked to water molecules through O-H...O and O-H...N hydrogen bonds.