In the title isonicotinohydrazide hydrate, C14H12BrN3O2·H2O {systematic name: N′-[(1E)-1-(5-bromo-2-hydroxyphenyl)ethylidene]pyridine-4-carbohydrazide monohydrate}, the central CN2O region of the organic molecule is planar and the conformation about the imine-C=N bond is E. While an intramolecular hydroxy-O—H...N(imine) hydrogen bond is evident, the dihedral angle between the central residue and the benzene rings is 48.99 (9)°. Overall, the molecule is twisted, as seen in the dihedral angle of 71.79 (6)° between the outer rings. In the crystal, hydrogen-bonding interactions, i.e. hydrazide-N—H...O(water), water-O—H...O(carbonyl) and water-O—H...N(pyridyl), lead to supramolecular ribbons along the a-axis direction. Connections between these, leading to a three-dimensional architecture, are mediated by Br...Br halogen bonding [3.5366 (3) Å], pyridyl-C—H...O(carbonyl) as well as weak π–π interactions [inter-centroid separation between benzene rings = 3.9315 (12) Å]. The Hirshfeld surface analysis reveals the importance of hydrogen atoms in the supramolecular connectivity as well as the influence of the Br...Br halogen bonding.