In the title hydrated salt, C4H12N2 (2+)·2C10H5O8 (-)·2H2O, the piperazinediium cation, lying about an inversion center, adopts a chair conformation. The benzene ring of the anion makes dihedral angles of 25.17 (8)° with the carboxyl-ate group and angles of 8.50 (7), 20.07 (7) and 80.86 (8)° with the three carb-oxy-lic acid groups. In the crystal, the cations, anions and water mol-ecules are connected by O-H⋯O and N-H⋯O hydrogen bonds into double layers parallel to (110).