This paper summarizes the characteristics of the Environmental Surveillance Radiological Networks (ESRN) currently operating in CEDEX. These networks include: Spanish Continental Waters ESRN, Spanish Costal Waters ESRN and the High Sensitivity Network in Continental and Marine Waters. It also presents the Radiological Surveillance of Drinking Waters that CEDEX carries out in waters of public consumption managed by the Canal de Isabel II (CYII) and by the Mancomunidad de los Canales del Taibilla (M.C.T). The legislation applicable in each case is reviewed as well. The paper has been divided in two parts due to his extension. In the first part, it presents the Spanish Continental Waters ESRN and in the second one the others ESRN.