The structural and dynamic properties of confined water in AlPO4-5 zeolite (circle divide = 7.3 Angstrom) have been investigated by neutron scattering experiments during the adsorption process. Our aim is to elucidate the peculiar behavior of confined water at the nanoscopic confinement range. Confined water presents unusual properties in comparison with other sorbate species such as deuterium or methane. Even in the nanoporous diameter range, the water sorption phenomenon looks like the so-called "capillary condensation" phase transition or the "dry-wet" transition. Furthermore, the sorbed water quantity in AlPO4-5 channels is exceptionally large. Our structural and dynamic results clearly show that the so-called "capillary condensation" step observed in the sorption isotherm is the signature of a crystallization phenomenon at room temperature (T = 300 K). It corresponds to the growth of two helices of ice of high density (d = 1.2) that is driven by structural commensurability with the AlPO4-5 channel structure.