The title compound, C14H13N3O3·H2O, adopts an E conformation with respect to the azomethine bond and crystallizes in the amide form. An intra­molecular O—H⋯N hydrogen bond occurs. In the crystal, the lattice water molecule plays a major role in the supramolecular architecture by interconnecting adjacent molecules into a three-dimensional netwrok by means of O—H⋯O, O—H⋯N and N—H⋯O hydrogen-bonding inter­actions. The structure also features two non-classical C—H⋯O inter­actions.

In the title compound, C12H11N3O3·2H2O, the dihedral angle formed by the planes of the pyridine and the furan rings of the organic carbohydrazide mol­ecule is 4.66 (7)°. In the crystal, these mol­ecules form stacks along the b-axis direction, neighbouring mol­ecules within each stack being related by inversion and the shortest distance between the centroids of the pyridine and furan rings being 3.714 (1) Å. Mol­ecules from neighboring stacks are linked by pairs of N—H⋯O hydrogen bonds. The water mol­ecules fill the channels between the stacks being linked by O—H⋯O hydrogen bonds into helices along [010]. Besides this, water mol­ecules are involved in O—H⋯N and O—H⋯O hydrogen bonds with the carbohydrazide mol­ecules, thus forming a three-dimensional network, augmented by weak C—H⋯O interactions.

The title compound, C15H12N4O, adopts an E conformation with respect to the azomethine bond and crystallizes in its hydrazinyl­idene tautomeric form. The dihedral angle between the ring systems is 15.98 (7)°. The phenol O—H group forms an intra­molecular O—H⋯N hydrogen bond. In the crystal, pairs of N—H⋯N and C—H⋯O hydrogen bonds link neighbouring mol­ecules into centrosymmetric dimers. These dimers are inter­connected by means of three types of π–π stacking inter­actions. One, with a centroid–centroid distance of 3.577 (1) Å [inter­planar separation = 3.4673 (6) Å], connects adjacent mol­ecules into centrosymmetric dimers. The other two inter­actions, on the outward facing sides of the dimers, are between phenol rings of neighboring mol­ecules [centroid–centroid separation = 3.7907 (13) Å and inter­planar separation = 3.5071 (8) Å], and between phthalazin units [centroid–centroid separation = 3.6001 (12) Å and inter­planar separation = 3.4891 (7) Å]. In combination, the π–π inter­actions lead to the formation of infinite layers with mol­ecules stacked along [0-11]. These layers are, in turn, connected with neighbouring layers through the N—H⋯N and C—H⋯O hydrogen bonds, yielding a three-dimensional supra­molecular architecture.