In the title compound, (n-C(4)H(9))(4)N(+)·C(7)H(5)O(3) (-)·2H(2)O, the carboxyl-ate group is twisted slightly out of the plane of the attached benzene ring, the two C-C-C-O torsion angles being -8.9 (2) and -10.7 (2)°. The anion inter-acts with two water mol-ecules through several O-H⋯O hydrogen bonds, forming wide ribbons along the a axis constructed from two anion-water chains. These ribbons are contained between unclosed diamond-like (16.2 × 15.0 Å) channels constructed by four rows of tetra-butyl-ammonium cations, which are arranged along the [011] and [01[Formula: see text]] directions.