2-Isopropyl-6-methyl-4-oxo-3,4-dihydro-pyrimidin-1-ium 2-carb-oxy-4,6-dinitro-phenolate monohydrate.

In the title mol-ecular salt, C(8)H(13)N(2)O(+)·C(7)H(3)N(2)O(7) (-)·H(2)O, the pyrimidinium cation is essentially planar, with a maximum deviation of 0.009†(1)†à . The cation undergoes an enol-keto tautomerism during the crystallization. In the crystal, the ion pairs and water mol-ecules are connected via O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds, forming two-dimensional networks parallel to the bc plane. There is an intra-molecular O-H⋯O hydrogen bond in the 3,5-dinitro-salicylate anion, which generates an S(6) ring motif.