A numerical model of water leak into vacuum through microcracks and crevices is proposed. A crevice is modeled by a long tube with a radius size of the order of 1 mu m. It is assumed that the water is in its liquid phase in the inlet, while it is in its gaseous phase in the outlet. In such a situation, the evaporation of water happens inside the tube when the water pressure reaches the pressure of saturated vapor. The molecular mean free path of vapor varies in a wide range along the tube so that the flow changes from the hydrodynamic to the free-molecular regime. Under such conditions, the water leak is calculated by combining the methods of rarefied gas dynamics and continuum mechanics. The leak rate is calculated for some values of the tube radius and several temperature gradients. The pressure distribution along the tube is also reported.