The rotational spectra of nine isotopomers of the 3-hydroxytetrahydrofuran-water complex were recorded using a Fourier transform microwave spectrometer. The spectra are assigned to the networked structure of the complex, with intermolecular hydrogen bonds from the hydroxyl to the water oxygen and from water to the furanose-ring oxygen. Ab initio calculations, at the MP2/6-31G** level, indicate that this is the lowest energy structure of the complex, and it is based on the lowest-energy ring-puckering conformation of the 3-hydroxytetrahydrofuran monomer, C-4 '-endo. Stark effect measurements were used to determine the projections of the dipole moment on the principal inertial axes: mu (a) = 1.2 (3) D, mu (b) = 1.8 (2) D, mu (c) = 0.7 (4) D, and mu (tot) = 2.2 (2) D.