Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. H atoms of the water mol­ecule and the NH2 group of the nicotinamide (NA) mol­ecule were located in a difference-Fourier map and refined freely. H atoms of the NH2 group of the 4-sulfomylbenzoate (SB) group were also located in a difference-Fourier map and the positions were refined with U iso(H) = 1.5U eq(N). The aromatic C-bound H atoms were positioned geometrically with C—H = 0.93 Å, and refined as riding with U iso(H) = 1.2U eq(C).