  Water ice is important for the evolution and preservation of life.
Identifying the distribution of water ice in debris disks is therefore of great
interest in the field of astrobiology. Furthermore, icy dust grains are
expected to play important roles throughout the entire planet formation
process. However, currently available observations only allow deriving weak
conclusions about the existence of water ice in debris disks. We investigate
whether it is feasible to detect water ice in typical debris disk systems. We
take the following ice destruction mechanisms into account: sublimation of ice,
dust production through planetesimal collisions, and photosputtering by
UV-bright central stars. We consider icy dust mixture particles with various
shapes consisting of amorphous ice, crystalline ice, astrosilicate, and vacuum
inclusions. We calculated optical properties of inhomogeneous icy dust mixtures
using effective medium theories, that is, Maxwell-Garnett rules. Subsequently,
we generated synthetic debris disk observables, such as spectral energy
distributions and spatially resolved thermal reemission and scattered light
intensity and polarization maps with our code DMS. We find that the prominent
$\sim$ 3 $\mu\rm{m}$ and 44 $\mu\rm{m}$ water ice features can be potentially
detected in future observations of debris disks with the James Webb Space
Telescope and the Space Infrared telescope for Cosmology and Astrophysics. We
show that the sublimation of ice, collisions between planetesimals, and
photosputtering caused by UV sources clearly affect the observational
appearance of debris disk systems. In addition, highly porous ice tends to
produce highly polarized radiation at around 3 $\mu\rm{m}$. Finally, the
location of the ice survival line is determined by various dust properties such
as a fractional ratio of ice versus dust, physical states of ice, and the
porosity of icy grains.
