  Infrared absorption spectroscopy study of endohedral water molecule in a
solid mixture of H$_2$O@C$_{60}$ and C$_{60}$ was carried out at liquid helium
temperature. From the evolution of the spectra during the ortho-para conversion
process, the spectral lines were identified as para- and ortho-water
transitions. Eight vibrational transitions with rotational side peaks were
observed in the mid-infrared: $\omega_1$, $\omega_2$, $\omega_3$, $2\omega_1$,
$2\omega_2$, $\omega_1 +\omega_3$, $\omega_2 +\omega_3$, and
$2\omega_2+\omega_3$. The vibrational frequencies $\omega_2$ and 2$\omega_2$
are lower by 1.6\% and the rest by 2.4\%, as compared to free \water/. A model
consisting of a rovibrational Hamiltonian with the dipole and quadrupole
moments of water interacting with the crystal field was used to fit the
infrared absorption spectra. The electric quadrupole interaction with the
crystal field lifts the degeneracy of the rotational levels. The finite
amplitudes of the pure $v_1$ and $v_2$ vibrational transitions are consistent
with the interaction of the water molecule dipole moment with a lattice-induced
electric field. The permanent dipole moment of encapsulated \water/ is found to
be $0.5\pm 0.1$ D as determined from the far-infrared rotational line
intensities. The translational mode of the quantized center of mass motion of
\water/ in the molecular cage of C$_{60}$ was observed at 110cm$^{-1}$
(13.6meV).
