4-Hy-droxy-2-methyl-1,1-dioxo-2H-1λ,2- benzothia-zine-3-carb-oxy-lic acid hemihydrate.

In the title compound, C(10)H(9)NO(5)S·0.5H(2)O, two geometrically different organic mol-ecules are present. The benzene rings and the carboxyl-ate groups are oriented at dihedral angles of 13.44 (4) and 21.15 (18)°. In both mol-ecules, an intra-molecular O-H⋯O hydrogen bond generates an S(6) ring. In the crystal, both moleucles form inversion dimers linked by pairs of O-H⋯O hydrogen bonds to generate R(2) (2)(8) loops. The dimers are consolidated into chains extending along [100] by bridging O-H⋯O hydrogen bonds from the water mol-ecule. A weak C-H⋯O hydrogen bond also occurs.