Currently, by the hydrological cycle, it is possible to observe that all water on Earth is somehow affected by human activities. With the prospect of increasing scarcity of drinking water, the decisions on where to exploit, use and manage water must be based on reliable information in order to protect this resource for future generations. In this context, the use of stable isotopes in hydrology enables interpretations of the origin and mechanisms of groundwater recharge, hydrograph separation, vertical leakage between aquifers, salinization risk and contamination of water resources, among others. Stable isotopes are useful in hydrological studies because of the physical-chemical reactions between various chemical species which cause isotopic fractionation of the same element between reactants and products. Data on δ18O and δ2 H reflect the values of the local average rainfall. These are generally modified by diffusion processes, which can change the isotope values before the water reaches the saturated zone. Its importance in relation to traditional hydrological studies is that stable isotopes are part of the water molecule itself, making the interpretations more accurate and independent of the degree of variability frequency of sampling. Nowadays, the integration of the largest possible number of chemical and isotopic tracers constitutes an important frontier of hydrological research and of integrated water resources management.