To provide a more refined insight into water availability and demand than is generally considered, a recent study (Hoekstra et al., 2012 ) has analysed the monthly Blue Water Footprint of 405 major river basins, in which 65 per cent of the global population reside.
A precautionary approach was taken based on natural flows (the estimated flow through the river basin before any water is taken out), and the presumed environmental flow requirement (the amount of water needed to maintain the integrity of freshwater ecosystems), assumed to be 80 per cent of monthly natural run-off (Richter et al., 2011).
If more than 20 per cent of the natural flow is being used by people, then the Blue Water Footprint is greater than the amount of blue water available and water stress will occur.
The Water Footprint provides a global indicator of both direct and indirect freshwater use
The focus on freshwater is important because it is scarce; making up only 2.5% of the water on the planet, 70% of which is locked up in the ice and snow of mountainous regions, the Arctic and Antarctic.
Whereas the Ecological Footprint calculates the amount of biocapacity (global hectares) needed to sustain a population, the Water Footprint of Production represents the volume of freshwater (in cubic metres per year, m3/y) used directly or indirectly to produce goods and services.
The darkest blue shading indicates river basins where more than 20% of water available in the basin is being used throughout the year. Some of these areas are in the most arid areas in the world (such as inland Australia) however other areas (such as western USA) have many months of water scarcity because significant amounts of water within these basins are being channelled into agriculture (Hoekstra et al., 2012).
Explore the Water Footprint of Production in different countries on the graph on the left (2010)