Abstract The method of material flux analysis is applied as an instrument for the early recognition of environmental problems in an urban region of developing countries. It is shown that, even with poor data quality and quantity, it is possible to apply the method in Tunja, an urban region in Colombia. With sensitivity analysis monitoring points are developed to attain 'early recognition' concerning changes in water quality and quantity in this region. Using the scenario technique it is shown that, owing to the low dilution capacity for sewage in the region, surface water cannot reach the quality of water at a natural state even if technical measures used in industrialized countries are taken.