In the title compound, 2C(3)H(7)N(6) (+)·C(4)H(4)O(6) (2-)·2H(2)O, in which the complete anion is generated by crystallographic twofold symmetry, there are O-H⋯O, N-H⋯O and N-H⋯N hydrogen-bonding inter-actions between neighbouring moieties, forming layers parallel to the bc plane. In addition, π-π contacts [centroid-centroid distance = 3.6541 (9) Å] between the six-membered rings of the melamine cations are observed.