The understanding of the occurrences of sub-surface waters, in quantity, quality and their hydrogeochemical interactions, necessarily goes through the understanding of the geological history, from the way and the environment in which the sediments were transported and deposited, in the case of sedimentary rocks, as well as how the magmatic and metamorphic rocks originated, including the structural features after their formation. It is important to stress that without this knowledge it becomes impractical to determine which types of reservoir rocks can be more or less productive in water. In the face of these issues, the role of the geologist in groundwater prospecting, understanding simultaneously its inter-relation with surface waters and climatic influences, is fundamental for the propositions of sustainable uses of these natural resources. On this issue, it is interesting to mention that it is highlighted in the "Universal Declaration of Water Rights", established by the UN on 22 March 1992, that water should not be wasted, polluted or poisoned.