Physical conditions in shocked regions of Orion from ground-based observations of H_2O

We present observations of the 5${}_{1,5}\to 4_{2,2}$ transition of water vapor at 325.15 GHz taken with the CSO telescope towards Orion IRc2. The emission is more extended than that of other molecular species such as CH${}_3$OH. However, it is much less extended than the emission of water vapor at 183.31 GHz reported by Cernicharo et al (1994). A comparison of the line intensities at 325.15 GHz and 183.31 GHz puts useful constraints on the density and temperature of the emitting regions and allows an estimate of H_2O abundance, x(H_2O), of $\simeq {10}^{-4}$ in the Plateau and $\simeq {10}^{-6}-{10}^{-5}$ in the Ridge.