UNSD/UNEP Questionnaires on Environment Statistics, Water section; Eurostat environment statistics main tables and database (http://epp.eurostat.ec.europa.eu/portal/page/portal/environment/introduction); and OECD Environmental Data Compendium, Inland Waters section, marked with " * ".
AQUASTAT database of the Food and Agriculture Organization of the United Nations (FAO); http://www.fao.org/nr/water/aquastat/water_res/index.stm. Whenever data were not available for the "Total renewable fresh water resources" variable from the UNSD or OECD/Eurostat Questionnaire, AQUASTAT data were used.
United Nations, Department of Economic and Social Affairs, Population Division, World Population Prospects: The 2008 Revision, New York, 2009 (advanced Excel tables).
- Data refer to average of 3 meteorological stations.
Data only includes surface water. Groundwater is excluded.
- Estimated value.
- The number is negative because evapotranspiration covers both water from precipitation and external inflow of water. Whereas precipitation covers water from rain that fall within the National territory.
- Data refer to the sum of inflows from Armenia and Turkey.
- Estimated availability (potential) from freshwater resources.
- Data refer to the Republic of Serbia without the territory of Kosovo Province.
- Data refer to years 1990-2005.
- Data refer to inflows from Lesotho and Swaziland.
- Excluding inflow of groundwaters.
- Renewable freshwater resources = internal flow, and inflow of surface and groundwaters is not included.
- The long-term annual average for precipitation, evapotranspiration and internal flow is based on a period of 13 years.
- The figures for internal flow include usable groundwater reservoirs, estimated at 22312 million m3.
- As annual figures for the inflow of surface and groundwaters are not available, the long-term annual average flow of surface waters from Colombia has been used.
Definitions & Technical notes:
Long term annual average is the arithmetic average over at least 20 years.
Precipitation refers to the total volume of atmospheric wet deposition (rain, snow, hail, dew, etc) falling on the territory of the country over one year, in millions of cubic metres.
Internal flow is the total volume of river run-off and ground water generated in natural conditions, exclusively by precipitation within the country. The internal flow is equal to precipitation less actual evapotranspiration and can be calculated or measured.
Renewable fresh water resources = Internal flow + Inflow of surface and groundwaters
Renewable fresh water resources per capita is calculated by UNSD by dividing the total renewable fresh water resources by the total population of the country.
Countrywide precipitation is usually calculated on the basis of measurements at a selected number of measuring stations within the country. Data are considered to be fairly reliable.
Internal flow is the fresh water generated in the country and is usually calculated by subtracting natural evapotranspiration from precipitation. The reliability of the data depends essentially on the estimation method for evapotranspiration.
For most countries, inflow of surface and ground water contains only the surface water flow, since ground water flows are often not well known. Surface water flows of inflowing rivers should be measured at the border. Dry countries in particular, tend to have reliable data.