Abstraction: The capture, diversion, taking of water for any purpose including an environmental purpose.

Allocation regime: The combination of policies, laws and institutional arrangements (entitlements, licenses, permits, etc.) used to determine who is allowed to abstract water from a resource pool, how much may be taken and when, as well as how much must be returned (of what quality), and the conditions associated with the use of this water.

Aquifer: Hydraulic continuous body of porous geological structure containing groundwater.

Groundwater depletion: See “unsustainable use”.

Groundwater development stress indicator (GDS): The ratio of groundwater abstraction for a given year to the mean annual groundwater recharge (including induced and artificial recharge) usually expressed as a percentage. It is a useful measure for the probability of the occurrence of negative side effects of groundwater depletion (Margat and van der Gun, 2013).

Groundwater system: A connected body of water located beneath the earth’s surface in soil pore spaces and/or in the fractures of rock formations.

Intensive development of groundwater: Development of the resource to such an extent to significantly change the natural flow in the aquifer or aquifer system (Margat and van der Gun, 2013).

Storativity: The amount of water released per unit area of aquifer in response to per unit decline in hydraulic head (Freeze and Cherry 1979 in Huang, et al 2012).

Sustainable yield: Flux of groundwater that can be withdrawn from an aquifer without causing undesirable side effects, in particular without causing a permanent state of imbalance in the hydrological budget of an aquifer (Margat and van der Gun, 2013).

Transmissivity: The speed of lateral flow of groundwater (Saak and Peterson, 2007).

Unsustainable use (also referred to as “over drafting” or “groundwater depletion”): Groundwater use beyond recharge capacity.

Usufructuary rights: The right of use of a resource or property and the enjoyment of benefits from that use. These use rights may be subject to conditions, such as the “reasonable” or “beneficial” use doctrine and limited to a pre-determined duration.

Water entitlement: The entitlement to abstract and use water from a specified resource pool as defined in the relevant water plan or legislation. In some countries, this may be referred to as “water rights”, “water users’ rights”, “water contracts”, abstraction license or permit.