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Actual/natural: The adjective qualifies the variable and indicates whether it corresponds to a natural situation, i.e. a measure of the water balance without human influence, or an actual situation, i.e. the conditions at a given time taking into account human influence either through uptake abstraction of water or through agreements or treaties. Natural conditions are considered stable over time while actual situations may vary with time and refer to a given period.

Average precipitation (mm/year and km3/year): Double average over space and time of the precipitation falling on the country in a year.

Average actual evapotranspiration (mm/year and km3/year): Double average over space and time of evaporation from water bodies, rivers and plants.

Dependency ratio (percent): That part of the total renewable water resources originating outside the country.

External renewable water resources (ERWR) (km3/year): That part of the country’s renewable water resources which is not generated in the country. The ERWR include inflows from upstream countries (groundwater and surface water), and part of the water of border lakes or rivers.

Exploitable water resources (km3/year) (also called manageable water resources or water development potential): The water resources considered to be available for development under specific economic and environmental conditions. The computation of exploitable water resources considers factors such as dependability of the flow, extractable groundwater, and minimum flow required for non-consumptive use.

Exploitation index (percent): Withdrawals of conventional freshwater resources (surface and groundwater) in relation to total renewable resources.

Internal renewable water resources (IRWR) (km3/year): Average annual flow of rivers and recharge of aquifers generated from endogenous precipitation.

Natural flow (km3/year): The amount of water that would flow in natural conditions, i.e. without human influence. It contrasts with actual flow, which takes into account upstream abstraction of water and treaties or agreement.

Non-conventional water resources: Total volume of water obtained through the development of new technologies. They are water generations (productions) that come either from desalination of sea and brackish waters or from wastewater regeneration for reuse.

Renewable resources: Total resources that are offered by the average annual natural inflow and runoff that feed each hydrosystem (catchment area or aquifer).

Total actual renewable water resources (TARWR) (km3/year): The sum of internal renewable water resources and incoming flow originating outside the country. The computation of TARWR takes into account upstream abstraction and quantity of flows reserved to upstream and downstream countries through formal or informal agreements or treaties. It is a measure of the maximum theoretical amount of water actually available for the country.

Total natural renewable water resources (km3/year): The sum of internal renewable water resources and natural incoming flow originating outside the country. It does not vary with time.

Total natural outflow (km3/year): Annual natural outflow of surface and groundwater from a country into the sea or a neighbouring country. The Aquastat calculation sheet considers only the outflow into the neighbouring countries (natural in general; actual where there is consumption in the country or reservation for downstream countries).


All renewable resources are long term annual averages.

(External) groundwater inflow (km3/year): Groundwater entering the country (usually limited to large aquifers shared by several countries, mostly in the arid zone).

(External) groundwater outflow (km3/year): Groundwater leaving the country either to the sea or to other countries (usually limited to large aquifers shared by several arid countries). The Aquastat calculation sheet considers only the outflow to neighbouring countries.

(External) surface water/outflow not submitted to agreements or treaties (km3/year): Average quantity of water leaving the country (including to the sea) and not submitted to treaties.

(External) surface water/flow of bordering rivers not submitted to agreements or treaties (km3/year): Surface water reaching the country through border rivers.

(External) surface water/outflow to be reserved through agreements or treaties (km3/year): Surface water to be reserved by treaty for a downstream country.

(External) surface water/inflow secured through agreements or treaties (km3/year): Part of the water entering the country that is secured through treaties.

(External) surface water/inflow not submitted to agreements or treaties (km3/year): Part of the external surface water inflow that is not submitted to formal agreements or treaties.

Overlap between surface water and groundwater (km3/year): That part of the renewable water resources which is common to both surface water and groundwater.

Total exploitable water resources (km3/year): A measure of the part of the resources that is considered available for development. Methods to assess exploitable water resources vary from country to country and depend on the country’s economic situation. Assessment of exploitable resources varies with time and should take into account the needs of the environment.

It may be subdivided in three subcomponents: regular surface water, irregular surface water, and regular groundwater.

Water availability (or available water resources): The terms water resources and water availability are often used as synonyms in the literature. However, these terms are not always defined clearly, leading to possible misinterpretation of the data. Some authors consider water availability to be the water not yet exploited in a given year, while others consider it closer to the concept of exploitable or manageable water resources. For the sake of clarity, the term water availability should be used in the sense of water net balance in a given state of use and exploitation of the resources and not with a meaning of water offer. The ‘availability’ may be: (i) equal to ‘resources’ minus ‘withdrawal’ at the local level of a subsystem, where a part of the water withdrawn cannot be returned into the system; or (ii) equal to ‘resources’ minus ‘final consumption’ at a more regional scale (watershed, country), where the balance encompasses all the use systems. This study avoids the term ‘water availability’ in an attempt to limit possible misinterpretations.


All the elements of the water balance are expressed in km3/year.

Area: 1 km2 = 100 ha

Volume: 1 km3 = 1 × 109 m3 = 1 000 × 106 m3 = 1 000 million m3.

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