3-Methyl-1,2,4-triazolo[3,4-a]phthalazine monohydrate.

In the crystal structure of the title compound, C(10)H(8)N(4)·H(2)O, the organic mol-ecules are approximately planar [maximum deviation from the least-squares plane = 0.041 (2) Å]. Two mol-ecules are connected by two water mol-ecules via O-H⋯N hydrogen bonding into dimers, which are located around centres of inversion. In the crystal, mol-ecules are stacked in the a-axis direction, with mean distances between the π systems of 3.43 (1) and 3.46 (1) Å [centroid-centroid distances are 3.604 (2) and 3.591 (2) Å].