Detailed water models predict the occurrence of water clusters, as configurations of water molecules whose total energy is a local minimum.
Of particular interest are the cyclic clusters (HO); these have been predicted to exist for n = 3 to 60.  
Research shows experimental result of the size of water cluster with 20 water molecules of 0.822 nm  Research uses of graph invariants for efficiently generating hydrogen bond topologies and predicting physical properties of water clusters and ice. The utility of graph invariants is confirmed by considering two water clusters, the (HO) cage and (HO) dodecahedron, which, associated with roughly the same oxygen atom arrangements in solid and liquid phases of water. At low temperatures, nearly 50% of water molecules are included in clusters.
With increasing cluster size the oxygen to oxygen distance is found to decrease which is attributed to so-called cooperative many-body interactions: due to a change in charge distribution the H-acceptor molecule becomes a better H-donor molecule with each expansion of the water assembly. Many isomeric forms seem to exist for the hexamer (HO): from ring, book, bag, cage, to prism shape with nearly identical energy.  Two cage-like isomers exist for heptamers (HO), and octamers (HO) are found either cyclic or in the shape of a cube.
Other theoretical studies predict clusters with more complex three-dimensional structures.  Examples include the fullerene-like cluster (HO), named the water buckyball, and the 280-water-molecule monster icosahedral network (with each water molecule coordinate to 4 others). The latter, which is 3 nm in diameter, consists of nested icosahedral shells with 280 and 100 molecules. There is also an augmented version with another shell of 320 molecules.  There is increased stability with the addition of each shell.   There are theoretical models of water clusters of more than 700 water molecules, but they have not been observed experimentally.