Crystals of the title compound, C(15)H(12)N(4)O·H(2)O, were obtained from a condensation reaction of isonicotinylhydrazine and 3-indolylformaldehyde. The mol-ecule assumes an E configuration, with the isonicotinoylhydrazine and indole units located on the opposite sites of the C=N double bond. In the mol-ecular structure the pyridine ring is twisted with respect to the indole ring system, forming a dihedral angle of 44.72 (7)°. Extensive classical N-H⋯N, N-H⋯O, O-H⋯O and O-H⋯N hydrogen bonding and weak C-H⋯O inter-actions are present in the crystal structure.