The lowest-lying excited rotational states of
 water can only be appreciably excited in the warmest,
 densest molecular clouds and cloud cores.  Molecular
 clouds in the region of the Galactic Center are
 particularly warm, so collisions with H2 molecules are
 sufficiently energetic throughout the clouds there to
 populate those low-lying levels and to thereby give rise to
 observable far-IR line emission.  We propose to observe four
 far-IR lines of water in galactic center clouds in order to:
 (1) determine the gas-phase water abundance in these clouds,
 (2) provide an independent measure of the cloud kinetic
 temperature using line ratios, and (3) infer the relative
 importance of water in the unusual thermal balance of these
 clouds.   This would represent the first concerted effort to
 study water in the Galactic center cloud population.

 Because the lines of interest occur in the far-infrared
 between 100 and 200 microns, they can only be observed with
 ISO and with the Kuiper Airborne Observatory (KAO).
 If the KAO continues operating beyond
 the 1994-95 season, this project would require multiple
 flights out of New Zealand, which NASA will be reluctant to
 grant because of the inordinate expense of operating there.
 In addition, the time required to measure four relatively
 weak lines in as many as 8 sources with the KAO is
 prohibitive, whereas it becomes a relatively routine
 observation for ISO.