Fourier-transform microwave spectroscopy was applied to observe the J = 1-0 rotational transition of the ortho-H-2-H2O complex and isotopologues in the ground Sigma(0) state (H-2 in the j(H2) = 1 state and H2O in the ground 0(00) state) to obtain precise molecular constants. Observed spectra were split into three hyperfine components, confirming the complexes are the ortho-H-2/para-D-2 species. The determined nuclear spin-spin coupling constant indicates H-2 is rotating almost freely in the complex; the Sigma(0) state is nearly of j(H2) = 1 and k(H2) = 0. For the ortho-H-2 species, the nuclear spin-rotation coupling constant was also determined. (C) 2014 Elsevier B.V. All rights reserved.