Given the importance of recycling and reusing water to mitigate issues related to droughts or urban floods and provide sustainable water usages, the current work aims to evaluate the Rainwater Harvesting (RWH) performance at a building scale, this method is based on the selection of five representative building types of the total stock within the city for which the efficiency of the rainfall water reservoir is going to be estimated. Hence, the present case study is applied to San Juan de Pasto, a medium city located at southwest of Colombia, where varied useful information was also analyzed such as the hydrological regime over time using data coming from three meteorological stations, as well as the dynamics of the population which is also related to demand patterns and water consumption.