The asymmetric unit of the title complex, {[Cd(C9H7N3O6S3)(C12H8N2)]·0.42H2O}n, contains a CdII atom, one doubly deprotonated 2,2′,2′′-[1,3,5-triazine-2,4,6-triyltris(sulfanediyl)]triacetic acid ligand (HTTTA2−), a 1,10-phenanthroline (phen) ligand and a fractionally occupied water molecule [site occupancy = 0.421 (15)]. The CdII atom is six-coordinated within a distorted octahedral coordination geometry. Six coordination arises from four O atoms derived from three different HTTTA2− ligands, and two N atoms of the chelating phen molecule. The incompletely deprotonated triazine ligand adopts a μ3-η1:η1:η2 coordination mode, resulting in the formation of chains along the c axis based on Cd2O2 dimeric units. Adjacent chains are stacked through π–π stacking [3.533 (2) Å between phen and triazine rings] and C—H⋯O interactions, forming supramolecular sheets in the ab plane. Intra-and intermolecular O—H⋯O hydrogen bonds are also observed.