The City of Wilmington is currently designing an upgrade to the conventional treatment process at their Brandywine Filtration Plant. The new process will include enhanced coagulation and ultrafiltration. During drought periods the plant will not be able to operate at its full capacity of 20 million gallons per day, due to a lack of source water from the Brandywine Creek. The excess treatment capacity could be used to pre-treat brackish water from a different source, thereby significantly reducing the cost to implement RO compared to a stand-alone RO facility. A study was performed to evaluate the feasibility, develop design criteria and determine budgetary cost of implementing RO at the upgraded Brandywine Filtration Plant. Results of the study indicated that potable water could be produced by the RO treatment system that would meet all drinking water regulations and that the current plant upgrade project will provide excellent pretreatment of the water prior to the desalination process. It is estimated that a new RO treatment system capable of producing 20 million gallons per day during drought conditions can be constructed for approximately $21 million if incorporated into the upgraded Brandywine Filtration Plant as currently designed, a cost savings of almost $40 million when compared to the stand-alone facility evaluated in 1997. The cost difference is due to utilization of the enhanced coagulation/ultrafiltration process for pre-treating the water prior to RO instead of constructing an entirely new pretreatment system. This paper includes background information on northern Delaware regional water supply issues and provides a brief description of the 20 mgd enhanced coagulation and ultrafiltration plant currently under design. Reverse osmosis treatment would be added to the plant to provide regional drought protection. Design criteria and budgetary costs are included. Permitting and environmental issues are also covered. Future project implementation steps and issues are discussed. Includes 4 references, tables, figure.