In the asymmetric unit of the title compound, C26H17N13O·C2H6OS·2H2O, there is one independent hepta-zine-based main mol-ecule, one dimethyl sulfoxide mol-ecule and two water mol-ecules as solvents. The tri-s-triazine unit is substituted with two dipyridyl amine moieties and a carbonylic O atom. As indicated by the bond lengths in this acid unit of the hepta-zine derivative [C=O = 1.213 (2) Å, while the adjacent C-N(H) bond = 1.405 (2) Å] it is best described by the keto form. The cyameluric nucleus is close to planar (r.m.s. deviation = 0.061 Å) and the pyridine rings are inclined to its mean plane by dihedral angles varying from 47.47 (5) to 70.22 (5)°. The host and guest mol-ecules are connected via N-H⋯O, O-H⋯O and O-H⋯N hydrogen bonds, forming a four-membered inversion dimer-like arrangement enclosing an R 4 (4)(24) ring motif. These arrangements stack along [1-10] with a weak π-π inter-action [inter-centroid distance = 3.8721 (12) Å] involving adjacent pyridine rings. There are also C-H⋯N and C-H⋯O hydrogen bonds and C-H⋯π inter-actions present within the host mol-ecule and linking inversion-related mol-ecules, forming a three-dimensional structure.