Laser induced fluorescence of microwave stimulated OH molecules from H2O photodissociation is investigated as a first step in a series of laboratory experiments to understand features of astronomical OH masers. The inversion between the Pi(3/2), J=7/2 Lambda-doublet states of OH generated via photodissociation of cold H2O at 157 nm is shown to be 1.8:1. Within a microwave, Fabry-Perot cavity tuned to the resonance of one of the main hyperfine transitions in this Lambda doublet it is possible to stimulate all inverted OH molecules. The linewidth of the two main microwave transitions is measured as a function of the microwave power and interaction time. The results show that Doppler broadening is negligible at short interaction times of the molecules with the microwave field.