In the title hydrated salt, C19H25N2(+)·I(-)·H2O, the 4-(diethyl-amino)-phenyl unit of the cation is disordered over two positions in a 0.847 (3):0.153 (3) ratio. The cation is twisted, with dihedral angles between the pyridinium and benzene rings of 11.25 (13) and 10.7 (8)° for the major and minor components, respectively. In the crystal, the three components are linked into a centrosymmetric 2:2:2 unit by O-H⋯I and C-H⋯O hydrogen bonds. π-π inter-actions with centroid-centroid distances of 3.5065 (7)-3.790 (9) Å are also present.