Increased irrigation, development, and population growth pose a potential threat to water supply in the Cabuyal River watershed in southwest Columbia. The landscape is characterized by steep hillsides with a patchwork of forest, pasture, and a variety of crops such as coffee, cassava, and irrigated vegetables. The International Center for Tropical Agriculture (CIAT) funded a project to develop a GIS-based, watershed-scale simulation model to evaluate a variety of development scenarios with respect to water supply for the year 2025. The authors concluded that there is enough water to support increased demand simulated in each of the development scenarios, but that management practices will determine if sufficient quantity is available at critical times.