Different legal systems conceive of groundwater differently and can vary along several dimensions. If a legal definitions is too narrow it can constrain the reach of the law, putting important resources beyond its control. On the contrary, if a definitions is too broad it could complicate administration of the law if it means that permission is required to undertake activities affecting resources that are not subject to concern about depletion or contamination. 

Key points of difference regarding the definition of groundwater include water in the saturated and unsaturated zone of the soil profile; whether it includes saline water solely or also freshwater, whether there is a depth limit to the water that is considered groundwater; the extent to which the definition includes things that are associated with groundwater, for example, like the aquifer structure, how to distinguish surface water and groundwater when they are subject to different allocation arrangements, whether to distinguish between naturally occurring groundwater and groundwater that has been artificially stored using managed aquifer recharge; and how different administrative units of groundwater are defined.