  Using heterodyne-detected optical Kerr effect (HD-OKE) measurements, we
investigate the vibrational dynamics and the structural relaxation of water
nanoconfined in Vycor porous silica samples (pore size $\simeq~4~nm$ ) at
different levels of hydration and temperatures. At low level of hydration,
corresponding to two complete superficial water layers, no freezing occurs and
water remains mobile at all the investigated temperatures with dynamic features
similar, but not equal, to the bulk water. The fully hydrated sample shows
formation of ice at about 248 K, this process does not involve all the
contained water; a part of it remains in a supercooled phase. The structural
relaxation times measured from the decay of the time-dependent HD-OKE signal
shows temperature dependence largely affected by the hydration level; the low
frequency ($\nu<500~cm^{-1}$) vibrational spectra, obtained by the Fourier
transforms of HD-OKE signal, appears less affected by confinement.

Soft Condensed Matter