The 4,4'-bipyridine molecules in the title compound, C10H8N2.2H2O, are stacked in the direction of the crystallographic b axis. These stacks are connected via O-H...N and O-H...O hydrogen bonds to form sheets which lie parallel to (100). Chains of O-H...O hydrogen-bonded water molecules are located between the bipyridine stacks. Altogether, four crystallographically independent water molecules and two crystallographically independent bipyridine molecules are involved.