A system to pump, treat, and inject surface water into selected aquifers through existing wells has been developed. The factors considered in the design of a system for recharging groundwater, and a procedure for evaluating potential groundwater recharge sites, are discussed. A pumping, treatment and injection system has been successfully field tested. In addition, laboratory studies to investigate the mixing process in aquifers, when lower density water is injected into higher density (saline) water, have shown that the injected slug of low density water does not readily mix with the higher density water. The technology developed in this research can be applied to improve the quality and the reliability of a groundwater supply.