In this paper we describe in detail the application of laser induced fluorescence (LIF) to the OH density measurement in a dielectric barrier discharge (DBD) at atmospheric pressure in Ar–H2O, He–H2O mixtures, and with small N2 additions. Measurements are reported in which OH density is measured in a pulsed DBD, together with its decay in the post-discharge. The variation of macroscopic discharge parameters, such as the applied voltage, the water vapour content, the gas mixture composition and the discharge duration, has a large effect on the OH loss rate and a smaller one on OH density. These effects are described and briefly discussed as a valuable help for the understanding of the complex microscopic kinetics of water containing discharges.