  We report the first measurement of size-resolved photoelectron angular
distributions for the valence orbitals of water clusters with up to 20
molecules. A systematic decrease of the photoelectron anisotropy is found for
clusters with up to 5-6 molecules, and most remarkably, convergence of the
anisotropy for larger clusters. We suggest the latter to be the result of a
local short-range scattering potential that is fully described by a unit of 5-6
molecules. The cluster data and a detailed electron scattering model are used
to predict liquid water anisotropies. Reasonable agreement with experimental
liquid jet data is found.
