There are clauses in the environmental license that define restrictions, requirements and measures of prevention and mitigation as conditions. These conditions-clauses have a role of damage prevention in the environmental licensing of an activity. The definition of these measures occurs within the public discretionary action of the environmental agency, which is limited by legal regulations applied. The present study deals with the importance of technical and scientific instruments present in environmental licensing as technical limits and materialization of the principle of proportionality in the definition of these conditions-clauses. These technical and scientific instruments work within the concept of technical discretionary in the administrative action in the field of study of Water Resources Law. From a study of four administrative processes of environmental licensing of mining activities in the Federal District in Brazil – obtained within the Brasília Environmental Institute – we studied the formation of conditions-clauses aimed at prevention, adaptation and mitigation of impacts on water resources from mining activities, while observing how these conditions-clauses are configured, reflecting on the limits of the technical and administrative action of the environmental agency. As a general conclusion, among the technical instruments that can guide the technical-administrative decision-making, those related to the prevention of water impacts are the Degraded Areas Recovery Plan, the Topographic and Recomposition Plan, the Monitoring and Hydrogeological Study, Drainage systems and Settling basins. Because they provide technical information on the affected area, they have shown direct relevance to the prevention of water impacts.