In the title compound, C16H13ClN2OS·H2O, the dihedral angle between the mean planes of the benzothiazole ring system and the methylphenyl ring is 79.3 (6)°. The crystal packing features intermolecular O—H⋯N, O—H⋯O and N—H⋯O hydrogen bonds involving the water molecule and weak C—H⋯O, C—H⋯Cg and π–π stacking interactions [centroid–centroid distances = 3.8743 (7), 3.7229 (7) and 3.7076 (8) Å].