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.

The title compound, C 21 H 18 N 2 O 3 , exists in the E conformation with respect to the azomethane C=N double bond. The central benzene ring is almost coplanar with one of the substituent benzene rings [dihedral angle = 1.74 (5)°] and is approximately orthogonal to the other benzene ring of the mol­ecule [dihedral angle = 86.61 (7)°]. An intra­molecular O—H⋯N hydrogen bond occurs. The crystal packing is dominated by N—H⋯O hydrogen bonds, which lead to an infinite chain running parallel to [010].