National water footprint accounting: moving beyond traditional statistics
Traditional national water use accounts only refer to the water withdrawal within a country. They do not distinguish between water use for making products for domestic consumption and water use for producing export products. They also exclude data on water use outside the country to support national consumption. In order to support a broader sort of analysis and better inform decision making, the national water use accounts should be extended. The scheme below is a visual representation of the national water footprint accounting scheme introduced by Hoekstra and Chapagain (2008).
The water footprint of national consumption is defined as the total amount of fresh water that is used to produce the goods and services consumed by the inhabitants of the nation. It consists of two components:
The virtual-water export from a nation is the total volume of freshwater consumed or polluted to produce the products for export. It consists of exported water of domestic origin and re-exported water of foreign origin. The virtual-water import into a nation will partly be consumed, thus constituting the external water footprint of national consumption and partly be re-exported. The sum of the virtual water import into a country and the water footprint within the area of the nation is equal to the sum of the virtual water export from the nation and the water footprint of national consumption. This sum is called the virtual-water budget of a nation.
A blue, green and grey water footprint
Water use is measured in terms of water volumes consumed (evaporated) and/or polluted per unit of time. The water footprint splits up into three elements:
Water self-sufficiency vs. water dependency
The ‘water self-sufficiency’ of a nation is defined as the ratio of the internal water footprint to the total water footprint of the nation. It denotes the national capability of supplying the water needed for the production of the domestic demand for goods and services. Self-sufficiency is 100% if all the water needed is available and indeed taken from within the own territory. Water self-sufficiency approaches zero if the demand for goods and services in a country is largely met with virtual-water imports. Countries with import of virtual water depend, de facto, on the water resources available in other parts of the world. The ‘virtual-water import dependency’ of a country or region is defined as the ratio of the external water footprint of the country or region to its total water footprint.