An ab initio and trajectory calculation is performed for the Penning ionization system H2O + He*(2(3)S) --> H2O+(B-2(2), (2)A(1), B-2(2)) + He + e(-). The Feshbach projection-operator method is employed to calculate the potential-energy surfaces (PES) of the resonance state and the partial widths for individual partial ionization. An attractive well near the oxygen lone pairs and a long-range barrier are found. The well is deeper but smaller than the corresponding well for H2O-He(2(3)S). Quasiclassical trajectory calculations are performed at H2O rotational temperatures of 300, 150, and 25 K based on the PES and the widths. The trajectories are drawn into an attractive H2O lone pair region less strongly with decreasing rotation frequency than those for the 2(3)S system. It is also found that fewer trajectories ionize at lower energy. These two results are due to the long-range barrier and the smaller well of the resonance PES for the present system.