An appreciation of the importance of water for the human society and of the possible negative impacts that human activities may exert on a resource that is not evenly distributed is instrumental to the understanding of the manner in which water laws and institutions have evolved over time and of the manner in which decisions as to new water policies, laws and institutional arrangements should be taken. These decisions should also consider the physical context, i.e., the characteristics and behaviour of water resources, whether surface or underground, as well as socio-economic aspects. Thus, the study of water law involves several disciplines, including hydrology, hydrogeology, economy and social sciences.