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==> In this proposal, more time is requested for JCERNICH.CERNI_1 For many years the extent of water emission and its abundance in molecular clouds have been key problems in the study of the interstellar medium (ISM). Although all chemical models predict a high water abundance, ground-based observations of non-masering rotational transitions of water are practically impossible. Recently, Cernicharo et al. (1990, 1994) succeeded in observing at 183 GHz the weakly masering 313-220 transition of water in many molecular clouds opening a new window to study water in the ISM. In particular, it was shown for the first time that water emission in Orion is spatially extended (see Fig 1). The derived abundances demonstrate that water is one of the most abundant molecular species in warm molecular clouds. In proposal CERNI_1, for which we obtained high priority time, we have observed SgrB2 and obtained spectacular results concerning the water extent and its excitation conditions (see Fig 2). We would like to increase the size of the raster obtained in SgrB2 and that of those that are being done now in other sources (from the same proposal CERNI_1). The main new source in this follow up is Ori-IRC2 which was our main source in the case of a spring launch of the ISO satellite. We would like to combine LWS01, LWS04 and SWS06 (vibrational bending band of water) observations on the proposed sources. ISO is the only instrument in the next decade which will allow to observe at high spatial resolution and sensitivity the thermal emission of water vapor in the ISM. The angular resolution of ISO in the far-infrared together with the sensitivity of the LWS FP spectrometer will enable to map and resolve the large scale distribution of water in molecular clouds. We propose to map several nearby molecular clouds in two lines of H2O connecting low-lying energy levels. Other transitions of water and its rare HH18O isotope (absolutely necessary in view of the large opacities involved in H2O) will be made towards selected positions in these molecular clouds. The proposed observations will provide a major contribution from ISO to our knowledge of the role of water in the chemistry and physics of the interstellar medium.