The insular town of Baru (Cartagena, Bolivar, Colombia) lacks aqueduct and sewer system services; however, Baru's habitants manipulate the water to satisfy their basic necessities. In this way, we evaluated water quality and characterized the dynamic of its use in Baru during the dry season (March of 2003). We answer two basic questions: is the available water in Baru suitable for human consumption? and, which are the events, flow and processes involved in its handling? The evaluation of the quality of the water was made by comparison of some physicochemical and microbiological variables versus the standards of the Colombian law. It was found that the water in Baru is not safe, due to coliforms. The dynamics of water use in this town was studied by interviewing some of the inhabitants and recognition trips of the available infrastructure. Information about consumption practices, habits and methods of treatment of sweet water, disposition of served waters and volume consumed by person (91,4 L/day) was obtained. With this information, we constructed a model of the water flow using the software STELLA 7.0.3®. It was found that the system has low sustainability due to the marked seasonality of rain, the great dependence to external factors and to the human work required for the maintenance of the system.