We propose to search for the features of H2O diluted in apolar ice
 towards sources obscured by dense clouds. The positions of these
 features are highly characteristic of the nature of the ice matrix,
 and a comparison of the observed spectra with laboratory data is
 therefore likely to provide important clues as to the chemical
 composition and morphological structure of interstellar ice mantles.
 The observation of such diluted H2O bands would be an excellent probe
 of the presence of infrared-inactive molecules
 like O2 and N2, which have been predicted to be abundant in
 interstellar ices. Information obtained in this manner could lead to
 a better understanding of the various processes shaping the icy grain
 mantles in dense clouds, such as the cloud's chemical evolution and
 gas-grain interactions through accretion and mantle desorption
 processes. ISO represents the perfect opportunity to observe the
 features of diluted H2O ice, since they fall in the spectral regions
 dominated by gas-phase telluric water (2.65 - 2.8 microns and 5.73 -
 6.58 microns) and are therefore unobservable with ground-based
 telescopes. These observations are intended to form a complementary
 data set to central program proposals (e.g. DWHITTET_ICE_BAND),
 filling up some major gaps with respect to wavelength coverage and
 object variety.