This paper deals with a spectroscopic characterization of an Ar-H2O discharge excited by a helical cavity at 27 MHz. The power and the pressure are fixed to 30 W and 266 Pa, respectively. Emissions from Ar, H, O atoms and the OH (A2Σ+→ X2Π) molecular spectral system are studied spatially along the discharge as a function of gas composition. Besides, weak emission of the second positive system of N2 coming from impurities is also detected. Conclusions are made about the possible role of argon and nitrogen metastable states in the excitation mechanism of the main emitting species. In addition to this, the characteristic temperatures are determined.