In the title compound, C(16)H(17)N(3)O·H(2)O, the isonicotinohydrazide mol-ecule adopts an E conformation about the central C=N double bond. The dihedral angle between the pyridine and the benzene rings is 54.56 (15)°. In the crystal, mol-ecules are connected via N-H⋯O, O-H⋯N and O-H⋯O hydrogen bonds, forming a three-dimensional network.