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Four salts, namely, 2,4,6‐triaminopyrimidinium 6‐chloronicotinate dihydrate, C4H8N5+·C6H3ClNO2−·2H2O, (I), 2,4,6‐triaminopyrimidinediium pyridine‐2,6‐dicarboxylate dihydrate, C4H9N52+·C7H3NO42−·2H2O, (II), 2,4,6‐triaminopyrimidinediium sulfate monohydrate, C4H9N52+·SO42−·H2O, (III), and 2,4,6‐triaminopyrimidinium 3,5‐dinitrobenzoate dihydrate, C4H8N5+·C7H3N2O6−·2H2O, (IV), were synthesized and characterized by X‐ray diffraction techniques. Proton transfer from the corresponding acid to the pyrimidine base has occurred in all four crystal structures. Of the four salts, two [(I) and (IV)] exist as monoprotonated bases and two [(II) and (III)] exist as diprotonated bases. In all four crystal structures, the acid interacts with the pyrimidine base through N—H...O hydrogen bonds, generating an R22(8) ring motif. The sulfate group mimics the role of the carboxylate anions. The water molecules present in compounds (I)–(IV) form water‐mediated large ring motifs. The formation of water‐mediated interactions in these crystal structures can be used as a model in the study of the hydration of nucleobases. Water molecules play an important role in building supramolecular structures. In addition to these strong hydrogen‐bonding interactions, some of the crystal structures are further enriched by aromatic π–π stacking interactions [(I) and (II)]. [ABSTRACT FROM AUTHOR]