The asymmetric unit of the title compound, C(20)H(24)N(2)O(4)·H(2)O, contains one half-organic mol-ecule (an inversion centre generates the other half of the mol-ecule) and a half-mol-ecule of water (the O atom has site symmetry 2). The near planarity of the fused-benzene ring is illustrated by the very small deviations of all the atoms from the plane [largest deviation = 0.0092 (11) Å. The six-membered N,O-containing ring adopts a half-chair conformation. The observed N-CH(2) and CH(2)-O bond lengths can be correlated to the manifestation of an anomeric effect in the N-CH(2)-O unit. In the crystal, the mol-ecules are connected into zigzag chains parallel to [001] through O-H⋯N hydrogen bonds formed between the oxazinic N atom and the solvent water mol-ecule. The chains are consolidated by C-H⋯O inter-actions.