Monte Carlo methods have been combined with end-bridging methods to study the solubility and structure of water in polyethylene, where the polyethylene contains a pair of oppositely charged ionic impurities. The water in the polymer is in equilibrium with pure liquid water. Both the polymer and pure water phases are exposed to an external electric field. The ions dramatically increase the solubility of water in polyethylene and induce the formation of a stable, rod-like water cluster between the ions. The solubility, the hydrogen-bond ordering of the water molecules in the cluster and the size of the cluster increase in the presence of an external field that enhances the local electric field between the ions. When the direction of the external field is reversed, and when it has the same magnitude as the local ionic field, the rod-like structure is broken up and a smaller cluster forms around each ion. (C) 2008 Elsevier Ltd. All rights reserved.