DETECTION OF HOT, ABUNDANT WATER TOWARD AFGL-2591

We present the first detection of absorption lines within the bending vibration of water in the interstellar medium using the ISO-SWS. More than 30 lines between 5.5 and 6.6 mu m are detected toward the bright infrared source GL 2591, which arise most likely in the dense molecula r cloud core surrounding the young stellar object. Comparison with mod el spectra indicates a high excitation temperature (T-ex > 200 K) and a high abundance [H2O]/[H-2] similar to (2 - 6) 10(-5). We speculate o n the origin of the hot water, and the consequences for the chemistry.