In the title compound, C16H15BrN2O4·H2O, the hydrazide molecule is nearly planar, with a largest deviation from the mean plane through the non-H atoms of 0.106 (4) Å and a dihedral angle between the benzene rings of 1.98 (16)°. This molecule adopts an E conformation about the C=N bond and an intramolecular O—H⋯N hydrogen bond increases the rigidity. In the crystal, some molecules of the title hydrazide are replaced by molecules of its 6-bromo isomer, and the Br atom from this admixture molecule was refined to give a partial occupancy of 0.0523 (13). The hydrazide and water molecules are linked through classical N—H⋯O and O—H⋯O hydrogen bonds, forming layers parallel to (110). C—H⋯π interactions are also present.