This publication is the result of long-term PhD research on hydrological and nutrient cycling in four undisturbed forest ecosystems in the Colombian Amazon. Amounts and dynamics of water fluxes in the forest compartments were followed by way of a monitoring programme and through models. Main findings are reviewed in terms of their implications for nutrient cycling and forest management. Differences were found between the amounts and dynamics of water storage capacity, water content, water uptake and drainage from the forest floor. The study provided relevant information on detailed climatic data and on the hydrological functioning of natural forest ecosystems in the Colombian Amazon, which can serve as a reference for impact studies and may support the development of sustainable forms of land use. Results from the present PhD study contribute to enlarging local knowledge related to the hydrological functioning of undisturbed forests in Colombian Amazonia and to a better understanding of related processes.