The asymmetric unit of the title compound, 2C(5)H(8)N(3) (+)·2C(2)HO(4) (-)·H(2)O, contains two crystallographically independent 2,6-diamino-pyridinium cations, a pair of hydrogen oxalate anions and a water mol-ecule. Both 2,6-diamino-pyridinium cations are planar, with maximum deviations of 0.011 (2) and 0.015 (1) Å, and are protonated at the pyridine N atoms. The hydrogen oxalate anions adopt twisted conformations and the dihedral angles between the planes of their carboxyl groups are 31.01 (11) and 63.48 (11)°. In the crystal, the cations, anions and water mol-ecules are linked via O-H⋯O and N-H⋯O hydrogen bonds, forming a three-dimensional network.