About hydrological planning One of the most important tasks of hydrological planning is water resources allocation and distribution among different water uses. The main water uses in Spain are urban use, agricultural, industrial not connected to the urban network and hydroelectric. Water resources are mainly found in rivers, reservoirs and groundwater. Due to the fact that Spain is mainly dry, nowadays it is really difficult to supply all the water demands from different uses and, at the same time, to satisfy the environmental objectives of the European Water Framework Directive (2000/60/EC). Thus, water resources allocation is done using balances between water resources and water demands, taking into account the priorities and management rules of water demands, the operation rules of infrastructures (dams, pipes and so on) and the environmental objectives. These water balances are done by simulations of a mathematical model that includes all the necessary data.