  The structure of water confined in MCM41 silica cylindrical pores is studied
to determine if confined water really is simply a version of the bulk liquid
which can be substantially supercooled without crystallisation. A combination
of total neutron scattering from the porous silica, both wet and dry,and
computer simulation using a realistic model of the scattering substrate isused.
The water in the pore is divided into three regions: core, interfacial and
overlap. The average local densities of water in these simulations are found to
be about 20% lower than bulk water density, while the density in the core
region is below, but closer to, the bulk density. There is a decrease in both
local and core densities when the temperature is lowered from 298K to 210K. The
radical proposal is made here that water in hydrophilic confinement is under
significant tension, around -100MPa, inside the pore.
