884 million people lacking access to safe drinking water, which contributes to 1.6 million deaths per year. This paper presents an application of Capacity Factor Analysis for the design of a rainwater harvesting system for Delmas 30, a small community in Port-au-Prince, Haiti. Capacity Factor Analysis is a decision aid for the selection of sustainable water supply infrastructure in developing communities. First, Capacity Factor Analysis was used to asses the management capability of the community and identify sustainable decentralized water supply technology options for increased access to drinking water. Rainwater harvesting was selected from the set of viable technology options. Next, a three part rainwater harvesting and treatment facility was designed for a centrally located community center. This design was informed by the results of the decision model. The designed rainwater catchment system is estimated to provide an additional 125,600 gallons of clean drinking water to the community of Delmas 30. The creation of an implementation plan, training program, and educational curriculum, along with the establishment of local supply chains, will serve to address areas low capacity identified by the decision model.