In the title hydrated hydrazine compound, C12H17N3O·H2O, the C=N bond adopts an E conformation. In the crystal, water molecules bridge the hydrazine molecules, via N—H...O and O—H...O hydrogen bonds, forming sheets parallel to the bc plane. There are C—H...π interactions present within the sheets, and further C—H...π interactions link the sheets to form a three-dimensional structure.