The water deficit occurring on an ever larger scale necessitates efficient use of existing water supplies using a network of artificial and natural water reservoirs to supply countries’ economic macro-regions with water. Many of these reservoirs are connected by rivers, canals or pipelines with water pumping stations, along with users consuming a particular water resources in a given hydrological area make economic water systems complex. A single water reservoir, as the primary object of a complex economic water system plays one of the most important roles in this area. Hence the need for a planned and safe execution of tasks, based on the relevant decisions concerning the regulation of the outflow of water from the reservoir and the proper use of its usable capacity. Controlling a complex system of reservoirs can be divided according to the type of decisions and time horizon to which they relate. The division identifies three main layers.