EARTHTRENDS DATA TABLES For more information, please consult http://earthtrends.wri.org TECHNICAL NOTES: FRESHWATER RESOURCES DEFINITIONS AND METHODOLOGY Internal Renewable Water Resources (IRWR) include the average annual flow of rivers and the recharge of groundwater (aquifers) generated from endogenous precipitation--precipitation occurring within a country's borders. IRWR are measured in cubic kilometers per year (km3/year). Groundwater Recharge is the total volume of water entering aquifers within a country's borders from endogenous precipitation and surface water flow. Groundwater resources are estimated by measuring rainfall in arid areas where rainfall is assumed to infiltrate into aquifers. Where data are available, groundwater resources in humid areas have been considered as equivalent to the base flow of rivers. Surface Water produced internally includes the average annual flow of rivers generated from endogenous precipitation (precipitation occurring within a country's borders). Natural incoming flow originating from outside a country's borders are not included in the total. Surface water resources are usually computed by measuring or assessing total river flow occurring in a country on a yearly basis. Overlap is the volume of water resources common to both surface and groundwater. It is subtracted when calculating IRWR to avoid double counting. Two types of exchanges create overlap: contribution of aquifers to surface flow, and recharge of aquifers by surface run-off. In humid temperate or tropical regions, the entire volume of groundwater recharge typically contributes to surface water flow. In karstic domains (regions with porous limestone rock formations), a portion of groundwater resources are assumed to contribute to surface water flow. In arid and semi-arid countries, surface water flows recharge groundwater by infiltrating through the soil during floods. This recharge is either directly measured or inferred by characteristics of the aquifers and piezometric levels. Total Internal Renewable Water Resources is the sum of surface and groundwater resources minus overlap. Actual Renewable Water Resources, gives the maximum theoretical amount of water actually available for each country, although in reality a portion of this water may be inaccessible to humans. Actual renewable water resources are defined as the sum of internal renewable resources (IRWR) and external renewable resources (ERWR). This takes into consideration the quantity of flow reserved to upstream and downstream countries through formal or informal agreements or treaties and possible reduction of external flow due to upstream water withdrawals. External renewable water resources (ERWR) are the portion of the country’s renewable water resources which is not generated within the country. The ERWR include inflows from upstream countries (groundwater and surface water), and part of the water of border lakes or rivers. Per Capita Actual Renewable Water Resources are measured in cubic meters per person per year (m3/person/year). Per capita actual water resources were calculated by WRI using the United Nations Population Division's World Population Prospects: The 2002 Revision. For more information about the collection methodology and reliability of the UN population data, please refer to the technical notes in the Deomgraphics and Education data table. Dependency Ratio is the percentage of total renewable water resources originating outside of the country. This indicator can be used to compare how different countries depend on external water resources. The dependency ratio may theoretically vary between 0 and 100 percent. A country with a dependency ratio equal to zero does not receive any water from neighboring countries. A country with a dependency ratio equal to 100 percent receives all its water from external sources without producing any. This ratio does not consider the possible allocation of water to downstream countries. Water Withdrawals (annual), measured in million cubic meters, is the gross amount of water extracted from any source, either permanently or temporarily, for a given use. It can be either diverted towards distribution networks or directly used. It includes consumptive use, conveyance losses, and return flow. Total water withdrawal is the sum of estimated water use by the agricultural, domestic, and industrial sectors. Per Capita Annual Withdrawals were calculated using national population data from the United Nations Population Division for the year 2000. Sectoral Withdrawals, expressed as a percentage, refers to the proportion of water used for one of three purposes: agriculture, industry, and domestic uses. All water withdrawals are allocated to one of these three categories. Agriculture uses of water primarily include irrigation and, to a lesser extent, livestock maintenance. Industry uses include cooling machinery and equipment, producing energy, cleaning and washing goods produced as ingredients in manufactured items, and as a solvent. Domestic uses include drinking water plus water withdrawn for homes, municipalities, commercial establishments, and public services (e.g. hospitals). Most Freshwater resources data were provided by AQUASTAT, a global database of water statistics maintained by the Food and Agriculture Organization of the United Nations (FAO). AQUASTAT collects its information from a number of sources--national water resources and irrigation master plans; national yearbooks, statistics and reports; reports from FAO; international surveys; and, results from surveys made by national or international research centres. In most cases, the information was analyzed to ensure consistency between the different data collected for a given country. When possible, cross-checking of information between countries was used to improve assessment in countries where information was limited. When several sources give different or contradictory figures, preference was always given to information collected at national or sub-national level. This preference is based on the assumption that no regional information can be more accurate than studies carried out at the country level. In general, official rather than unofficial sources were used. In the case of shared water resources, a comparison between countries was made to ensure consistency at river-basin level. Industrial Water Pollution, shown here in average metric tons per day is measured by biochemical oxygen demand (BOD), which refers to the amount of oxygen, in kilograms per day (kg/day), that bacteria in water will consume in breaking down waste. For example, an overload of sewage in natural waters exhausts the water's dissolved oxygen content. Low levels of dissolved oxygen in water can impact the health of aquatic resources and ecosystems. BOD is a standard water-treatment test that determines the difference between the final dissolved oxygen concentration and the initial dissolved oxygen concentration. This difference represents the oxygen consumed (or BOD) in breaking down the organic materials in the sample. A 1998 World Bank study carried out by Hettige, Mani, and Wheeler used plant and sector-level information on organic discharge (measured by BOD) and employment from 13 national environmental protection agencies and sector-level information on output and employment from the United Nations Industrial Development Organization (UNIDO). Their economic analysis found that the ratio of BOD to employment in each industrial sector is about the same across countries. This finding allowed the authors to estimate BOD intensities per unit of employment across countries and over time. Multiplying these estimates by sectoral employment numbers from UNIDO's industry database for 1980 to 1998 provides sectoral emissions, which were then used to calculate daily emissions of organic water pollutants (BOD) per day. These data were later updated through 2000 using the same methodology. For further information, please refer to the Hettige, Mani, and Wheeler print publication, which is availabile online at: http://www.worldbank.org/nipr/work_paper/kuznet/kuznets.pdf. FREQUENCY OF UPDATE BY DATA PROVIDERS AQUASTAT was developed by the Food and Agriculture Organization of the United Nations in 1993; data have been available on-line since 2001. Most freshwater data are not available in a time series, and the global data set contains data collected over a time span of up to 30 years. AQUASTAT updates their website as new data become available, or when FAO conducts special regional studies. Most data updates include revisions of of past data. World Development Indicators is updated and published annually by The World Bank. DATA RELIABILITY AND CAUTIONARY NOTES While AQUASTAT represents the most complete and careful compilation of country-level water resources statistics to date, the primary information on which it relies is of variable quality. Information sources are various but rarely complete. Some governments will keep internal water resources information confidential because they are competing for water resources with bordering countries. Many instances of water scarcity are highly localized and are not reflected in national statistics. In addition, the accuracy and reliability of information vary greatly among regions, countries, and categories of information, as does the year in which the information was gathered. As a result, no consistency can be ensured among countries on the duration and dates of the period of reference. All data should be considered order-of-magnitude estimates. Groundwater Recharge is sometimes overestimated in arid areas and underestimated in humid areas. Actual Renewable Water Resources vary with time. Exchanges between countries are complicated when a river crosses the same border several times. Part of the incoming water flow may thus originate from the same country in which it enters, making it necessary to calculate a "net" inflow to avoid double counting of resources. In addition, the water that is actually accessible to humans for consumption is often much smaller than the total renewable water resources indicated in the data table. Actual Renewable Water Resources Per Capita contains water resources data from a different set of years than the population data used in the calculation. While the water resources data are usually long-term averages, inconsistencies may arise when combining it with 2002 population data. For more information about the collection methodology and reliability of the UN population data, please refer to the Demographics and Education table. Industrial Water Pollution focuses on organic water pollution resulting from industrial activities only. Organic matter can also come from sources that are not as easily identifiable as those associated with industrial activities. Such sources are known as non-point sources and some examples include agricultural runoff and livestock operations. These non-point sources can contribute significantly to the oxygen demand in water and are not represented by the data displayed here. Water pollution tends to be sensitive to local conditions. As such, the national level data may not reflect the quality of water in specific locations. BOD is typically measured in a laboratory environment, where it is difficult to reproduce ambient conditions like temperature, sunlight, and water movement; therefore the measurement should be considered an estimate. SOURCES Renewable Water Resources, Dependency Ratio, and Water Withdrawals: Food and Agriculture Organization of the United Nations (FAO), Water Resources, Development and Management Service. 2003. AQUASTAT Information System on Water and Agriculture: Review of World Water Resources by Country. Available on-line at http://www.fao.org/waicent/faoinfo/agricult/agl/aglw/aquastat/water_res/index.htm. Rome: FAO. Population Data (for per capita calculations): Population Division of the Department of Economic and Social Affairs of the United Nations Secretariat. 2003. World Population Prospects: The 2002 Revision. New York: Per capita actual water resources were calculated by WRI using the United Nations Population Division's World Population Prospects: The 2002 Revision. United Nations. Data set on CD-ROM. Industrial Water Pollution: The World Bank, Development Data Group. 2004. World Development Indicators. Available on-line at http://www.worldbank.org/data/. Washington: The World Bank.