In the title compound, [[Zn(C8H4O5)(C12H8N2)].H2O]n or [[Zn(OH-BDC)(phen)].H2O]n (where OH-H2BDC is 5-hydroxyisophthalic acid and phen is 1,10-phenanthroline), the Zn atoms are coordinated by two N atoms from the phen ligands and by four O atoms from hydroxyisophthalate ligands in a highly distorted octahedral geometry, with Zn-O distances in the range 2.042 (4)-2.085 (5) A and Zn-N distances of 2.133 (5) and 2.137 (5) A. The [[Zn(OH-BDC)(phen)].H2O]n infinite zigzag polymer forms a helical chain of [Zn2(OH-BDC)2]n units. Face-to-face pi-pi interactions (3.60-3.75 A) occur between two phen rings belonging to the same helical chain. Consolidation of the packing structure is achieved by O-H...O hydrogen-bonding interactions between the carboxylate O atoms, the hydroxyl group and the water molecule, forming two-dimensional sheets.