Water confined to a repulsive ellipsoidal cavity with a variable aspec
t ratio is studied by computer simulation. The orientational order par
ameter of the O-H bond with respect to the symmetry axis of the cavity
, S-OH,is examined as a function of the cavity dimensions for finite n
umbers of water molecules (N = 6 to 38 at constant density). We observ
e that the absolute value of S-OH is increased by deforming a spherica
l cavity into either a prolate or an oblate ellipsoidal cavity. This t
rend is method independent, i.e., it is obtained using Monte Carlo sim
ulations with TIP4P or SPC water and using molecular dynamics simulati
ons. Generally \S-OH\ decreases with increasing N and temperature for
a fixed cavity aspect ratio. The calculated magnitudes of S-OH and its
temperature dependence are in order-of-magnitude agreement with exper
imental NMR determinations of S-OH in hydrated fibers. Hence such spat
ial anisotropies should be considered in models of the residual orient
ation exhibited by probe molecules in fibrous synthetic and biological
materials.