The title compound, C(17)H(12)N(2)O·H(2)O, was synthesized by the reaction of 4,5-diaza-fluoren-9-one with a Grignard reagent in ether (the reaction mixture being hydrolysed with saturated NH(4)Cl solution), and crystallizes with two organic mol-ecules and two water mol-ecules in the asymmetric unit. The 4,5-diaza-fluorene fragment is approximately planar, with r.m.s. deviations of 0.0448 and 0.0198 Å in the two mol-ecules. The dihedral angles between the 4,5-diaza-fluorene planes and the phenyl ring are 80.49 (6) and 76.57 (7)°. The crystal packing features O-H⋯N and O-H⋯O hydrogen bonds involving the bridging solvent water mol-ecules, which link the mol-ecules into a three-dimensional network.