4-{[3-(4-Hydroxy-benzyl-ideneamino)-2,2-dimethyl-propyl]iminiomethyl}phenolate dihydrate.

The asymmetric unit of the title compound, C(19)H(22)N(2)O(2)·2H(2)O, comprises a zwitterionic form of the Schiff base compound and two water mol-ecules of crystallization. Inter-molecular N-H⋯O, C-H⋯O and O-H⋯N hydrogen bonds involving one of the water mol-ecules in the asymmetric unit generate seven- and eight-membered rings, with R(2) (1)(7) and R(2) (2)(8) ring motifs, respectively. The dihedral angle beween the two aromatic rings is 86.5 (2)°. The imino and iminium groups are coplanar with the benzene rings to which they are attached, making dihedral angles (N-C-C-C) of -179.3 (5) and -179.2 (4)°, respectively. Validation software indicates the higher symmetry space group Pnma for this structure. However, this process ignores H atoms and the zwitterionic configuration of the main mol-ecule breaks the higher symmetry. Solution in Pna2(1) provides a chemically sensible zwitterionic compound with improved residuals. In the crystal structure, mol-ecules are linked together through inter-molecular O-H⋯O, O-H⋯N, N-H⋯O and C-H⋯O inter-actions, forming a three-dimensional network. The crystal structure is further stabilized by inter-molecular C-H⋯π inter-actions.