In the title compound, (CH(3))(4)N(+)·0.5C(8)H(4)O(4) (2-)·2H(2)O, the complete terephthalate dianion is completed by twofold symmetry and has a dihedral angle of 23.5 (2)° between the carboxyl-ate group and its parent ring. Two independent water mol-ecules serve as both donors and acceptor in the construction of undulating hydrogen-bonded host layers with various O-H⋯O contacts ocurring between the anion and two water mol-ecules. At the same time, the tetra-methyl-ammonium cations, as the sphere-like guest species, are arranged in two rows between neighboring host layers, with an approximate inter-layer distance of 7.36 Å, forming a sandwich-like crystal structure.