Water is a strategic resource to explore and produce hydrocarbons.The study of groundwater resources to characterize/ define "aquifer systems" and the elaboration of hydrogeologic conceptual models that allow their knowledge, are the main tools to understand the hydrogeology of any region. When the zone is more arid and its geology more complex, the systems are more difficult to understand and thus the models to elaborate. When more data and results are obtained and evaluated systematically with experience in hydrogeologic conceptual models, they are elaborated with increasing certainty and detail. With them, decisions can be taken with more certitude from the points of view of the "sustainable use of the resource" and the "environmental" one, applying the paradigm of Integrated Water Resource Management (IWRM), within the Sustainable Development. If there is not a previous hydrogeologic conceptual model, it is impossible to make a mathematical model for simulation, because there is not a reliable base to elaborate it.The characterization and definition of an aquifer system should have its classic components: aquifers themselves (porous, high to medium permeability), aquitards (porous, low permeability), aquicludes (porous, impermeable), aquifugues (nonporous, impermeable), fractured aquifers (originally may have been aquicludes/ aquifugues, but by fracturing they have transformed in aquifers due to secondary porosity and permeability); recharge, circulation and discharge areas; flow systems of different scales (regional, subregional, local). When the knowledge reached allows it, they may include: hydrogeochemistry zonations, evolution with groundwater flow and increasing depth, isotopic characterization, origins and ages of water.The characterization of aquifer systems and hydrogeologic conceptual models allow to elaborate maps and vertical sections useful as tools to make decisions. If the studied region/ zone of an aquifer system is large and variable, there may be differences between distinct areas, each of them having a particular hydrogeologic conceptual model, compatible with the regional one. There may be zones where the aquifer system acts in general as one complex flow unit, and others where it is compartmentalized: divided by aquicludes ("seals") and/or aquitards ("semiseals") which allow to discriminate distinct bodies/ thicknesses with different characteristics.If the knowledge reached and the data/ results are enough, hydrogeologic conceptual models can be expressed in Petrel or Sahara format or similar, allowing to be managed with friendly tools by geologists and other professionals of hydrocarbon industry not specialists in hydrogeology.Examples of aquifer systems and hydrogeologic conceptual models from argentine hydrocarbon basins in arid/ semiarid regions are presented, with different levels of knowledge and scales.